Neonatal herpes simplex virus infection: Clinical features and diagnosis

INTRODUCTION — Herpes simplex virus (HSV) infection during pregnancy poses a significant risk to the developing fetus and newborn. Neonates can acquire HSV infection by intrauterine, perinatal, or postnatal transmission of the virus; most cases are acquired perinatally. Neonatal HSV infection causes serious morbidity and mortality and leaves many survivors with permanent sequelae. Strong clinical suspicion, timely diagnosis, and early antiviral treatment are critical to improving outcome.

The clinical features and diagnosis of neonatal HSV infection will be reviewed here. The management, outcome, and prevention of neonatal HSV infection and genital HSV infection during pregnancy are discussed separately. (See "Neonatal herpes simplex virus infection: Management and prevention" and "Genital herpes simplex virus infection and pregnancy".)

VIROLOGY — HSV is a member of the Herpesviridae family of viruses. It contains a double-stranded linear deoxyribonucleic acid (DNA) genome that consists of 150,000 base pairs that encode for more than 80 polypeptides, a capsid consisting of 162 capsomeres arranged in icosahedral symmetry that is covered by a tightly adherent membranous tegument, and an envelope consisting of 11 glycoproteins (gB, gC, gD, gE, gG, gH, gI, gJ, gK, gL, and gM), lipids, and polyamines that surrounds the viral nucleocapsid (picture 1) [1]. Like all Herpesviridae viruses, HSV shares the biologic properties of latency and reactivation, which causes recurrent infections in the host.

HSV enters the human host through inoculation of oral, genital, nasal, or conjunctival mucosa or breaks in skin, then infects the sensory nerve endings, and then transports via retrograde axonal flow to the dorsal root ganglia, where it remains for the life of the host. The fetus may be infected transplacentally or through retrograde spread through ruptured or seemingly intact membranes [1]. Latent virus is not susceptible to antiviral drugs, and infection (even after antiviral therapy) is lifelong. (See "Neonatal herpes simplex virus infection: Management and prevention", section on 'Outcome'.)

HSV replicates efficiently in cell cultures, quickly producing lytic cytopathic effect in one to three days in most cell lines used in virology laboratories (picture 2). The virus can be typed into HSV type 1 and HSV type 2 using serologic and molecular techniques. The DNA of HSV-1 and HSV-2 contain many homologous sequences distributed over the entire genome of both types, which produce both unique (gG) and antigenically similar polypeptides [1]. This cross-reactivity between HSV-1 and HSV-2 glycoproteins is the reason many commercially available serologic assays cannot reliably distinguish between HSV-1 and HSV-2 antibodies. Diversity in genes encoding certain viral proteins may correlate with clinical disease manifestations in the neonate. In particular, genes that impact neurovirulence and viral spread between cells (eg, glycoprotein G [gG; US4], I [GI; US7], and K [GK; UL53], and viral proteins UL8, UL20, UL24, and US2) have been associated with more severe neuroinvasive disease in preliminary studies [2].

EPIDEMIOLOGY AND TRANSMISSION

Incidence and prevalence — The estimated incidence of neonatal HSV infection ranges from 3 to 30 per 100,000 live births [3-8]. The wide variation is likely due to differences in the prevalence of genital herpes in different areas around the world and differences in reporting practices. In the United States, the annual incidence is approximately 8 to 10 cases per 100,000 live births [3,8]. Globally, there are an estimated 14,000 cases of neonatal HSV infection per year [9].

The prevalence of HSV among young infants presenting to an emergency department setting with signs of central nervous system (CNS) infection was investigated in a multicenter retrospective study of >25,000 infants <60 days old (median age 28 days) who underwent lumbar puncture for evaluation of fever or other clinical concern [10]. Testing for HSV was performed in 35 percent of patients. HSV infection was identified in 1.2 percent of infants tested (0.4 percent of the entire cohort), 39 percent of whom had skin, eye, and mouth (SEM) disease, 32 percent of whom had CNS disease, and 29 percent of whom had disseminated disease. HSV prevalence peaked in the second week of life and declined substantially in the second month of life. Despite the low prevalence of HSV in this setting, testing and empiric treatment for HSV are often warranted in ill-appearing febrile neonates because early treatment has been shown to improve survival and reduce long-term sequelae. This issue is discussed briefly below and is reviewed in greater detail separately. (See 'Clinical suspicion' below and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy' and "The febrile infant (29 to 90 days of age): Management", section on 'Herpes simplex virus' and "The febrile neonate (28 days of age or younger): Outpatient evaluation and initial management", section on 'Herpes simplex virus infection'.)

Trends over time — The incidence of neonatal HSV disease appears to have modestly increased since the early 2000s [8]. One reason for this is that the prevalence of genital HSV infection appears to be increasing in the general population. In particular, HSV-1 genital infection among adolescents and young adults (AYAs) appears to be increasing, and thus neonatal HSV-1 infection may be increasing [9]. The result is that a greater proportion of neonatal HSV disease in the contemporary era is due to HSV-1 rather than HSV-2. Neonates with HSV-1 disease are more likely to present with SEM disease, whereas HSV-2 disease is more commonly associated with CNS disease [9,11]. (See "Epidemiology, clinical manifestations, and diagnosis of genital herpes simplex virus infection", section on 'Epidemiology'.)

The evolving epidemiology of neonatal HSV disease was described in a single-center study from 1980 to 2016 [9]. The following changes were observed over the course of the study:

●Beginning in 2010, HSV-1 eclipsed HSV-2 as being the more common viral type for neonatal infection

●Since 2010, more infants presented with SEM disease; whereas before 2010, most affected neonates presented with CNS or disseminated disease

●The average time from onset of symptoms to diagnosis and initiation of treatment decreased from approximately 6 to 8 days in the earlier eras to approximately 3 to 4 days in the contemporary era

●Mortality decreased from approximately 20 percent in the earlier eras to 5 percent in the contemporary era

Transmission — Neonatal HSV has three distinct periods of acquisition: intrauterine, perinatal, and postnatal.

●Intrauterine – Approximately 5 percent of neonatal HSV infections are caused by intrauterine infection. Viral infection occurs in the fetus before birth and disease manifestations are present at birth.

●Perinatal – The majority (85 percent) of neonatal HSV infections are acquired perinatally [12]. HSV is acquired perinatally when HSV infection, either symptomatic or asymptomatic, is present in the genital tract of the pregnant woman at the time of delivery.

Factors that may influence perinatal transmission include [13]:

•Type of maternal HSV infection (primary maternal HSV infection is associated with higher risk of transmission to the neonate compared with recurrent)

•Maternal HSV antibody status

•Duration of ruptured membranes

•Use of fetal scalp monitors

•Mode of delivery (cesarean versus vaginal, although neonates born via cesarean may still develop neonatal HSV disease)  

However, most neonates with HSV disease are born to mothers without a history of HSV infection or other identifiable risk factors [14]. Maternal fever is a risk factor for neonatal HSV infection [14-19]. (See "Genital herpes simplex virus infection and pregnancy", section on 'Vertical transmission'.)

●Postnatal – Approximately 10 percent of neonatal HSV infections are acquired postnatally [12]. Postnatal acquisition of neonatal HSV occurs from direct contact with a family member or other close contact with active HSV infection, such as herpes labialis [20,21]. There are isolated case reports of sibling transmission when one sibling has gingivostomatitis and kisses or bites the newborn [20]. Postnatally acquired HSV infection can be especially severe in newborns born to women without prior HSV infection [20]. This is because such newborns will not have received transplacental transmission of HSV-specific antibody.

CLINICAL MANIFESTATIONS

Intrauterine HSV — Intrauterine or congenital HSV infection is rare and results from either maternal viremia associated with primary HSV infection during pregnancy or ascending infection:

●Intrauterine infection due to maternal primary infection – Intrauterine infection that results from maternal primary HSV infection and viremia during pregnancy is associated with placental infarcts; necrotizing, calcifying funisitis (inflammation of the umbilical cord); plasma cell deciduitis; lymphoplasmacytic villitis (picture 3); hydrops fetalis; and fetal in utero demise. Demonstration of the virus in placenta tissue by immunohistochemistry or by molecular techniques is necessary for diagnosis of HSV involvement of the placenta because other placental findings are nonspecific. (See "Nonimmune hydrops fetalis" and "Stillbirth: Incidence, risk factors, etiology, and prevention".)

Liveborn neonates with intrauterine HSV infection may exhibit a characteristic triad of [22-25]:

•Skin vesicles, ulcerations, or scarring (picture 4)

•Eye damage

•Severe central nervous system (CNS) manifestations, including microcephaly, cystic encephalomalacia, or hydranencephaly

However, the characteristic triad occurs in less than one-third of cases, and a high index of suspicion is necessary to make the diagnosis [25].

●Intrauterine infection due to ascending infection – In utero congenital HSV infection from ascending infection usually occurs after prolonged rupture of membranes in mothers with active HSV infection near the time of delivery. Ascending transplacental infection of the fetus through intact amniotic membranes may also occur, and neonatal HSV infection has been documented after cesarean section in mothers with intact amniotic membranes [26,27]. The clinical presentation of newborns with intrauterine HSV acquired by ascending infection may be mild, with only cutaneous skin lesions or cutaneous scarring present, to severe, with signs and symptoms of disseminated HSV disease and fatal neonatal pneumonitis [28,29].

Neonatal HSV — Perinatally and postnatally acquired neonatal HSV may be classified into three main categories for therapeutic and prognostic purposes (table 1):

●Localized skin, eye, and mouth (SEM) disease only (see 'Skin, eye, and mouth disease' below)

●CNS disease (with or without SEM) (see 'Central nervous system disease' below)

●Disseminated disease (see 'Disseminated disease' below)

There is some overlap in these categories (figure 1). For example, disseminated HSV disease may have SEM and/or CNS involvement in addition to other organs, and SEM disease may progress to CNS or disseminated disease if not treated early. Both HSV-1 and HSV-2 may cause SEM, CNS, or disseminated disease; however, HSV-1 is more likely to be associated with SEM disease, while HSV-2 is associated more often with CNS disease and with a poorer outcome [1,9,13,15,30]. (See "Neonatal herpes simplex virus infection: Management and prevention", section on 'Outcome'.)

Skin, eye, and mouth disease — SEM disease accounts for approximately 35 to 45 percent of neonatal HSV [6,9]. Neonatal HSV SEM disease may appear benign at onset of illness but is associated with a high risk of progression to CNS or disseminated disease if not treated. SEM disease usually presents in the first two weeks of life but may occur at any time during the first six weeks of life [31].

Localized skin disease is associated with coalescing or clustering vesicular lesions with an erythematous base (picture 5C) [1]. Vesicles may begin or cluster at the presenting part of the body, or at sites of localized trauma, such as scalp monitor sites (picture 5B). Skin vesicles also may appear late in the course of disseminated disease.

HSV infection of the eye may initially appear asymptomatic. In the neonate, early signs include excessive watering of the eye, crying from apparent eye pain, and conjunctival erythema (picture 5A). Periorbital skin vesicles may or may not be present at the time of presentation. HSV keratoconjunctivitis may progress to corneal scarring, cataracts, and chorioretinitis and result in permanent vision impairment [1,22].

HSV infection of the oropharynx may initially be asymptomatic but also may be characterized by localized ulcerative lesions of the mouth, palate, and tongue. It should be differentiated from other causes of oral lesions in the newborn such as local trauma or other viral infections (eg, enterovirus). (See "Soft tissue lesions of the oral cavity in children", section on 'Infections' and "Soft tissue lesions of the oral cavity in children".)

Neonates and infants up to six weeks of age with evidence of SEM disease should undergo a thorough evaluation for CNS and disseminated disease. Infants with SEM disease may have associated HSV viremia. However, if there is no evidence systemic disease (eg, no liver, lung, kidney, cardiovascular, or CNS involvement), most experts would not consider such infants as having disseminated HSV disease. If SEM disease is treated early, before CNS or disseminated disease occurs, the outcome is favorable. (See 'Detection of HSV' below and 'Laboratory evaluation' below and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Outcome'.)

Central nervous system disease — Approximately one-third of neonatal HSV disease involves the CNS [9,31]. It may occur as a result of localized retrograde spread from the nasopharynx and olfactory nerves to the brain or through hematogenous spread in neonates with disseminated disease. Neonatal HSV CNS disease (also called neonatal HSV meningoencephalitis) usually presents in the second or third week of life, but may occur at any time during the first six weeks of life [31]. CNS disease may occur with or without SEM involvement and with or without disseminated disease. Between 60 and 70 percent of neonates with HSV CNS disease have skin vesicles at some point during the disease course [12].

Clinical manifestations of neonatal HSV CNS disease include seizures (focal or generalized), lethargy, irritability, tremors, poor feeding, temperature instability, and full anterior fontanel [30,32,33]. Early in the course of HSV CNS disease, none of these signs or symptoms may be apparent.

Cerebrospinal fluid (CSF) analysis in neonates with HSV CNS disease classically shows a modest mononuclear cell pleocytosis, normal or moderately low glucose concentration, and mildly elevated protein; however, CSF studies may be normal early in the course of the illness. Abnormalities of the CSF may be more pronounced as CNS disease progresses. Red blood cells are not significantly associated with neonatal HSV CNS disease and are more likely to be caused by an apparent "bloody tap" [14].

The electroencephalogram (EEG) often is abnormal very early in the course of CNS disease and may show lateralized periodic discharges (LPDs, previously called periodic epileptiform discharges [PLEDS]) [1,34]. (See 'Electroencephalogram' below.)

Computed tomography (CT) and magnetic resonance imaging (MRI) of the brain may be normal early in the course of CNS disease. Several days to a week into illness, neuroimaging studies may show parenchymal brain edema or attenuation, hemorrhage, or destructive lesions involving the temporal, frontal, parietal, or brainstem regions of the brain (image 1 and image 2) [1,32]. (See 'Diagnostic imaging' below.)

In the absence of vesicles, the initial presentation of HSV CNS disease may be indistinguishable from other causes of neonatal sepsis or meningitis [12,35]. Many experts recommend evaluation for HSV CNS disease with HSV DNA polymerase chain reaction (PCR) and other CSF studies (ie, cell counts, protein, and glucose), and empiric treatment with acyclovir in all neonates with aseptic meningitis or other signs and symptoms of meningoencephalitis without an obvious bacterial cause [36,37]. (See 'Laboratory evaluation' below and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy'.)

Neonates with certain underlying primary immune disorders (eg, functional natural killer [NK] cell deficiencies, toll-like receptor deficiencies) are at risk for developing severe HSV encephalitis and postinfectious complications such as HSV-mediated autoimmune encephalitis [38]. (See "NK cell deficiency syndromes: Clinical manifestations and diagnosis" and "Toll-like receptors: Roles in disease and therapy", section on 'UNC93B1 deficiency, TLR3 mutations, TRIF deficiency, TRAF3 deficiency, and TBK1 deficiency'.)

Disseminated disease — Approximately 25 to 30 percent of neonatal HSV disease is the disseminated form, which is sepsis-like presentation, involving multiple organs [9,19,31]:

●Liver (picture 6 and picture 7), including hepatitis with elevated liver transaminases, ascites, and direct hyperbilirubinemia that can progress to liver failure requiring liver transplantation [39]. (See "Acute liver failure in children: Etiology and evaluation" and "Acute liver failure in children: Management, complications, and outcomes".)

●Lungs (picture 8), including progressive interstitial pneumonitis and hemorrhagic pneumonitis, with or without effusion, that can progress to respiratory failure, requiring mechanical ventilation or extracorporeal life support [40].

●CNS, which is involved in 60 to 75 percent of cases, usually through a hematogenously acquired meningoencephalitis [31]. (See 'Central nervous system disease' above.)

●Heart, including myocarditis and myocardial dysfunction in severe disseminated neonatal HSV.

●Adrenal glands (picture 9 and picture 7).

●Bone marrow and coagulation system, including disseminated intravascular coagulation (DIC), thrombocytopenia, and neutropenia. (See "Disseminated intravascular coagulation in infants and children".)

●Kidneys. (See "Neonatal acute kidney injury: Pathogenesis, etiology, clinical presentation, and diagnosis".)

●Gastrointestinal tract, including necrotizing enterocolitis. (See "Neonatal necrotizing enterocolitis: Clinical features and diagnosis".)

●Skin and mucous membranes lesions, which may appear late in the course of disseminated HSV disease; however, 20 to 40 percent of neonates with disseminated HSV disease do not have vesicles [12]. (See 'Skin, eye, and mouth disease' above.)

Neonates with disseminated HSV often present in the first week of life with nonspecific signs and symptoms of neonatal sepsis, including temperature dysregulation (fever or hypothermia), apnea, irritability, lethargy, respiratory distress, abdominal distension, hepatomegaly, and ascites [1,19]. Rarely, neonates with HSV infection may present with fever alone [41]. In advanced disseminated neonatal HSV disease, fever is often absent, and hypothermia is more prominent [1,19].

The diagnosis of disseminated neonatal HSV disease often is delayed until the second week of life, awaiting the results of evaluation for bacterial sepsis. In treated infants, the risk of mortality associated with disseminated HSV infection is approximately 40 to 50 percent; in untreated infants, mortality exceeds 80 percent [9]. Unfortunately, the diagnosis is sometimes made or confirmed at autopsy, after extensive organ damage has occurred (picture 7 and picture 6 and picture 8 and picture 9). Efforts are focused on identifying high-risk neonates with a sepsis-like picture, meningoencephalitis, progressive pneumonitis, or hepatitis, who should undergo testing for HSV and empiric antiviral therapy [14,18,42,43]. (See 'Evaluation and diagnosis' below and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy'.)

EVALUATION AND DIAGNOSIS

Overview — Neonatal HSV infection is clinically challenging. Early manifestations may be subtle and nonspecific. Neonatal HSV can mimic other diseases, including bacterial illnesses (sepsis or meningitis), other viral illnesses (particularly enterovirus), and genetic/metabolic disorders of infancy. Prompt treatment requires early consideration of neonatal HSV as a possibility in neonates with mucocutaneous lesions, central nervous system (CNS) abnormalities, a sepsis-like picture, progressive hepatitis, or coagulopathy. (See 'Differential diagnosis' below and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy'.)

Clinical suspicion — Neonatal HSV infection should be suspected in neonates and infants up to six weeks of age with [31,44]:

●Mucocutaneous vesicles or ulcers (picture 5A-C)

●Sepsis-like illness (fever or hypothermia, irritability, lethargy, respiratory distress, apnea, abdominal distension, hepatomegaly, ascites, coagulopathy)

●Cerebrospinal fluid (CSF) pleocytosis, especially with a mononuclear predominance

●Seizures

●Focal neurologic signs

●Abnormal neuroimaging

●Respiratory distress, apnea, or progressive pneumonitis

●Thrombocytopenia

●Elevated liver transaminases, viral hepatitis, or acute liver failure

●Conjunctivitis, with watery discharge, excessive tearing, or painful eye symptoms, especially if unilateral

Early in the clinical course, some neonates with HSV infection may present with persistent fever and negative bacterial cultures.

Neonatal HSV infection remains a possibility in infants born to mothers who received suppressive acyclovir therapy during pregnancy. Although suppressive therapy markedly reduces the risk of asymptomatic shedding, it does not completely eliminate it. Neonates with perinatal exposure to HSV (particularly maternal active genital lesions, but also postnatal direct exposure to individuals with active HSV oral lesions) should be monitored for evidence of HSV infection (algorithm 1). (See "Neonatal herpes simplex virus infection: Management and prevention", section on 'Management of asymptomatic exposed infants'.)

Detection of HSV — The laboratory diagnosis of neonatal HSV infection may be established through isolation of HSV in traditional or enhanced viral culture, detection of viral DNA using qualitative or quantitative polymerase chain reaction (PCR) assays, and detection of viral antigens using rapid direct immunofluorescence assays (DFA). Serology is generally not helpful in the diagnosis of neonatal HSV at the time of presentation.

Specimens to collect — Neonates with suspected HSV disease should have all of the following specimens obtained to evaluate for HSV infection [31]:

●Surface swabs – Swab specimens should be collected from the conjunctivae, mouth, nasopharynx, and rectum. Some experts suggest obtaining these with a single swab, starting with eyes and ending with the rectum, and placed in one viral transport media tube. Alternatively, they may be collected with multiple swabs and processed separately or placed in a single viral transport media tube and processed together. Regardless of how the specimens are collected, they should be tested with PCR and viral culture. (See 'Skin and mucous membrane' below and 'Viral culture' below.)

●Swabs/scrapings of skin lesions – If the neonate has lesions on the skin or mucous membranes, swabs/scrapings/aspirate of vesicle fluid should be obtained and tested with PCR and viral culture. DFA of skin lesion scrapings may permit rapid detection of HSV; however, DFA is not as sensitive as culture or PCR. (See 'Skin and mucous membrane' below and 'Viral culture' below and 'DFA and EIA' below.)

●CSF – All neonates with suspected HSV, even infants who appear to have isolated skin, eye, and mouth (SEM) disease, should undergo lumbar puncture because clinical findings may be absent early in the course of CNS disease. PCR is the test of choice for detection of CNS involvement. (See 'Cerebrospinal fluid' below.)

●Blood or plasma – Neonates with suspected HSV disease, of any classification, should have a whole blood or plasma sample tested for HSV using PCR. (See 'Blood' below.)

●Other specimens – Viral culture or HSV PCR should be performed on other specimens that are readily available (eg, tracheal aspirates in intubated infants, peritoneal fluid in neonates undergoing peritoneal drainage or laparotomy for other reasons). (See 'Viral culture' below.)

●Additional studies – Additional testing should be performed to assess the degree of organ involvement, as discussed below. (See 'Additional studies' below.)

Viral culture — Isolation of HSV by viral cell culture and serotyping HSV-1 or HSV-2 was traditionally the standard for definitive diagnosis of neonatal HSV infection. However, in the current era, many diagnostic virology laboratories and clinical reference laboratories offer PCR assays, which are an accurate and rapid method for detection and diagnosis of HSV infection. (See 'Polymerase chain reaction' below.)

Surface cultures (ie, from skin lesions, conjunctivae, mouth, nasopharynx, and rectum) are positive in ≥90 percent of cases and provide the greatest diagnostic yield of all methods to detect HSV, regardless of disease classification [30]. Isolation of HSV from surface sites of the neonate obtained >12 to 24 hours after birth indicate viral replication and are suggestive of infection, rather than contamination from intrapartum exposure. This is the most common and noninvasive method to obtain evidence of active neonatal HSV infection [1,31].

Isolation of HSV by viral culture of other specimens (eg, CSF, blood, tracheal aspirates, duodenal aspirates, peritoneal fluid in neonates with ascites) can also establish the diagnosis, but these are less commonly performed. For CSF and blood samples, PCR is preferred over viral culture because it has greater sensitivity. The sensitivity of viral culture for detecting CNS involvement is low (approximately 25 to 40 percent) [45]. (See 'Cerebrospinal fluid' below and 'Blood' below.)

HSV grows readily on most cell lines used in clinical diagnostic virology laboratories. Evidence of viral cytopathic effect (picture 1) is usually evident under light microscopy in one to three days. Fresh vesicular lesions of the skin often are positive within 24 hours of incubation, whereas isolation from CSF or other sites may require several days. Viral cultures that remain negative at 10 days usually remain negative. HSV isolated in cell culture can be quickly and reliably typed as HSV-1 or HSV-2 using commercially available type-specific immunofluorescence assay reagents.

Twenty-four-hour cell culture enhancement systems, such as shell vial centrifugation fluorescent foci cultures (SVC) and enzyme-linked virus inducible systems (ELVIS), are used in many clinical laboratories and provide rapid detection of HSV in clinical systems within 24 to 48 hours [46,47]. The performance of these systems is generally comparable to cell culture in detecting HSV in skin and mucous membrane lesions, but not all these assays are able to distinguish and type HSV-1 or HSV-2.

Polymerase chain reaction

Cerebrospinal fluid — PCR is the test of choice for detection of CNS involvement and has a sensitivity of 75 to 100 percent and specificity 71 to 100 percent [45]. The detection of HSV DNA in the CSF of a neonate confirms the diagnosis of CNS involvement. CSF HSV PCR is more sensitive than viral culture; however, blood or high protein in the CSF may interfere with some PCR assays and produce false negative results [48-53]. False negative results have also been reported with CSF specimens obtained early in the course of illness and samples obtained several days into antiviral therapy [1,48,50,53]. If the initial CSF HSV PCR is negative, yet neonatal HSV CNS disease is strongly suspected, the CSF PCR should be repeated during the first week of illness [54]. In neonates with evidence of CNS involvement, such as seizures, focal neurologic signs, abnormal CSF, or abnormal brain imaging, the detection of HSV DNA confirms the diagnosis of HSV meningoencephalitis. However, neonates may have CNS HSV infection without overt clinical, laboratory, or imaging signs of meningoencephalitis. Approximately 25 percent of neonates with HSV apparently localized to the SEM, and more than 90 percent of neonates with disseminated HSV disease, have HSV DNA detected in their CSF by PCR [1]. Thus, it is imperative to include a CSF examination and CSF HSV PCR in all neonates with suspected or proven neonatal HSV infection.

Quantitative HSV PCR can be performed on CSF samples, but studies have not confirmed that the level of HSV DNA by PCR correlates with neurologic outcomes [55].

Blood — In neonates with signs and symptoms of disseminated HSV disease, detection of HSV DNA in the blood or plasma confirms the diagnosis and provides the opportunity for early initiation of antiviral therapy [1,14,43,52,55,56]. Results may differ somewhat depending on the sample type (whole blood versus plasma) and type of assay (qualitative versus quantitative).

Quantitative HSV PCR, if available, can be useful for several reasons:

●It may detect HSV infection

●It distinguishes the viral type (HSV-1 versus HSV-2)

●It quantifies the level of HSV viremia, which correlates with disease severity [55]

In a study of 63 infants treated for neonatal HSV at a single institution (1993 to 2012), plasma HSV PCR was positive in 78 percent of neonates with SEM, 64 percent with CNS disease, and 100 percent with disseminated disease [55]. Quantitative plasma HSV PCR levels were highest in infants with disseminated disease and levels >7 log₁₀ copies/mL were associated with an increased risk of death.

Skin and mucous membrane — Many hospital-based and reference laboratories offer validated HSV PCR assays for skin and mucous membrane surface samples (ie, from skin lesions, conjunctivae, mouth, nasopharynx, and rectum). PCR assays on mucosal specimens, including multisource surface swabs, are an accurate and rapid method to detect HSV-1 or HSV-2 in neonates [31,57,58].

Other sites — PCR testing of other samples may be helpful in certain circumstances:

●In intubated patients, detection of HSV DNA in tracheal aspirates can help support a diagnosis of HSV pneumonitis.

●Detection of HSV DNA in amniotic fluid is diagnostic of in utero or congenital HSV.

●In neonates with necrotizing enterocolitis managed with peritoneal drainage or laparotomy, detection of HSV DNA in peritoneal fluid provides evidence of HSV disease.

●Detection of HSV DNA in the eye or conjunctivae may help establish the diagnosis of neonatal blepharoconjunctivitis or keratitis due to HSV, particularly in neonates in whom pretreatment with antiviral ophthalmic drops or systemic therapy may influence the viral culture results.

DFA and EIA — DFA and enzyme immunoassays (EIA) methods permit rapid detection of HSV antigens in skin and mucous membrane lesions [47,59]. DFA has high specificity for HSV infection, and typing of the HSV antigens may be done directly on material on the slide. However, DFA is not as sensitive as PCR since the accuracy of DFA depends on the adequacy of the specimen (ie, it must contain sufficient cells) and the skill of the technician [59].

EIA is primarily used to screen asymptomatic or pregnant people for HSV genital infection [59]. Use of rapid EIA for diagnosis of neonatal HSV infection is not recommended since its performance in this setting is not well established.

Serology — Serologic tests generally are not helpful in the diagnosis of neonatal HSV infection but may be used in the following circumstances:

●To identify HSV-2 infection in pregnant people so that steps can be taken to prevent neonatal infection. (See "Genital herpes simplex virus infection and pregnancy".)

●To confirm the diagnosis of neonatal HSV infection when there is diagnostic uncertainty during the newborn period. Persistence of HSV type-specific immunoglobulin G (IgG) antibody beyond the time period of transplacental IgG antibody duration (ie, beyond six months) can help confirm the diagnosis if direct detection of the virus at the time of illness was not successful or possible.

Interpretation/diagnosis — Interpretation of diagnostic testing for HSV in neonates depends upon the clinical circumstances (table 1). Most infected infants have positive viral culture and/or PCR in one or more of the specimens listed above. (See 'Specimens to collect' above.)

Similarly, infants with negative viral culture/PCR in all of the above listed specimens are unlikely to be infected with HSV. However, in the setting of highly suggestive clinical, laboratory, or radiologic findings, negative results do not exclude HSV infection.

●SEM disease – The diagnosis of SEM disease is based upon the following clinical and laboratory parameters:

•Localized skin disease with the characteristic vesicular lesions (picture 5C and picture 5B); eye involvement; and/or localized ulcerative lesions of the mouth, palate, and tongue, and

•Absence of CNS disease (including negative CSF HSV PCR) or other organ system involvement, and

•One or more of the following:

-Detection of HSV by viral culture, PCR, or DFA in surface swabs or skin lesion swabs/scraping collected >12 to 24 hours after birth (present in >90 percent)

-Positive HSV DNA PCR in the blood or plasma (present in 75 to 80 percent and does not necessarily signify disseminated disease if there are no signs of systemic illness or end organ involvement)

●CNS disease – The diagnosis of CNS disease is based upon the following clinical, laboratory, and radiographic parameters:

•Positive CSF HSV DNA PCR (present in 75 to 100 percent; if the initial CSF HSV PCR is negative, yet neonatal HSV CNS disease is strongly suspected, the CSF PCR may be repeated during the first week of illness)

or

•Clinical evidence of CNS involvement (eg, seizures, abnormal neurologic examination, abnormal EEG, and/or abnormal neuroimaging), and

•Either or both of the following:

-Detection of HSV by viral culture, PCR, or DFA in surface swabs or skin lesion swab/scraping collected >12 to 24 hours after birth (present in >90 percent)

-Positive HSV DNA PCR in the blood or plasma (present in approximately 65 percent)

●Disseminated disease – The diagnosis of disseminated disease is based upon the following clinical, laboratory, and radiographic parameters:

•Clinical signs of systemic involvement (eg, severe sepsis syndrome, hepatitis, pneumonia, disseminated intravascular coagulation, and/or thrombocytopenia), and

•One or more of the following:

-Detection of HSV by viral culture, PCR, or DFA in surface swabs or skin lesion swabs/scraping collected >12 to 24 hours after birth (present in >90 percent of neonates with SEM disease)

-Positive HSV DNA PCR in the blood or plasma (present in nearly all cases)

-Positive CSF HSV DNA PCR (present in up to 90 percent)

Additional studies — A comprehensive evaluation should be performed in all neonates with suspected or proven HSV disease. This evaluation is necessary, even in infants who appear to have isolated SEM disease because clinical findings may be absent early in the course of CNS and disseminated disease. In addition to routine laboratory tests, ophthalmologic examination and neuroimaging should be performed in all infants with virologically confirmed HSV infection, and EEG should be performed in neonates with CNS involvement [1,32]. (See 'Electroencephalogram' below and 'Diagnostic imaging' below.)

Laboratory evaluation — Laboratory evaluation in neonates with suspected or proven HSV disease includes all of the following tests which determine the degree of organ involvement and exclude other diseases that may cause similar clinical symptoms [1,14,31,43] (see 'Differential diagnosis' below):

●Complete blood count, including differential and platelet count.

●Liver transaminases, total and direct bilirubin, ammonia (ammonia should be performed to exclude liver failure and metabolic disease in neonates with elevated liver enzymes and fulminant sepsis but is not necessary for all neonates with suspected HSV).

●Blood urea nitrogen (BUN), creatinine, and urinalysis (to assess renal function and hydration status).

●CSF cell count, glucose, and protein.

●Blood and CSF cultures to evaluate for possible bacterial sepsis (most neonates with neonatal HSV disease have negative blood cultures; however, bacterial coinfections can occur, especially in neonates with liver and intestinal involvement, where gram-negative bacteremia, sepsis, or peritonitis may compound the clinical presentation of neonatal HSV). (See "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates" and "Bacterial meningitis in the neonate: Clinical features and diagnosis".)

●Evaluation for metabolic disease as indicated by the clinical scenario. (See "Inborn errors of metabolism: Epidemiology, pathogenesis, and clinical features" and "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management".)

Eye examination — All infants with neonatal HSV disease, regardless of disease classification, should have an ophthalmologic examination in addition to conjunctival HSV cultures to evaluate for eye involvement [31].

Electroencephalogram — EEG should be performed in all neonates suspected to have CNS involvement, particularly those with seizures, abnormal movements suspicious for seizures, or abnormal CSF.

EEG is highly sensitive for neonatal HSV infection with CNS involvement and often is abnormal before CT or MRI. An abnormal EEG with lateralized periodic discharges (LPDs; formerly called periodic lateralized epileptiform discharges [PLEDS]) is a characteristic finding in neonatal HSV encephalitis [34]. However, LPDs are nonspecific and can be seen in other types of brain injury.

Diagnostic imaging

Brain imaging — All infants with neonatal HSV disease, regardless of disease classification, should have neuroimaging with MRI, CT, or ultrasonography [31]. In neonates with suspected or proven CNS involvement, brain imaging with enhanced CT or MRI is recommended to determine the location and extent of brain involvement [1,32]. Contrast-enhanced MRI with diffusion-weighted imaging (DWI) is preferred over CT or noncontrast MRI because it is more sensitive than CT [32]. However, CT is acceptable if MRI cannot be readily performed. A normal CT or conventional MRI early in the course does not exclude HSV CNS involvement since subtle findings may only be detected with DWI. Head ultrasound should not be used as the sole imaging study in infants with clinical evidence of CNS disease since neonatal ultrasound often underrepresents the extent of brain involvement. However, prenatal ultrasound may show fetal brain damage in intrauterine HSV disease.  

The imaging findings of neonatal HSV CNS disease are variable. Neuroimaging may be normal early in the course of CNS disease. Several days to a week into illness, neuroimaging may show parenchymal brain edema or abnormal attenuation, hemorrhage, or destructive lesions (image 1 and image 2) [1,32]. In addition to the classic temporal lobe destructive lesions, imaging abnormalities may be multifocal or limited to the brainstem or cerebellum [34]. Long-term sequelae of neonatal HSV CNS involvement includes atrophy and cystic encephalomalacia.

Chest radiograph — Chest radiographs should be obtained in infants with signs of pulmonary involvement. In neonates with lung involvement, chest radiographs may demonstrate bilateral, diffuse pneumonitis.

Abdominal ultrasonography — Abdominal ultrasonography is not routinely required in the diagnostic evaluation. In neonates with HSV hepatitis and acute liver failure, ultrasonography may demonstrate liver enlargement, ascites, or complex fluid collections consistent with peritonitis.

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of neonatal HSV is broad and includes infectious and noninfectious conditions that are associated with vesicular skin lesions, eye disease, central nervous system (CNS) manifestations, and/or systemic illness in neonates:

●Vesicular skin lesions – The differential diagnosis of vesicular skin lesions in neonates is reviewed separately. (See "Vesicular, pustular, and bullous lesions in the newborn and infant" and "Skin lesions in the newborn and infant".)

●Eye disease:

•Viral conjunctivitis due to adenovirus or enterovirus (see "Conjunctivitis", section on 'Viral conjunctivitis')

•Bacterial conjunctivitis (eg, Chlamydia trachomatis, Neisseria gonorrhoeae) (see "Chlamydia trachomatis infections in the newborn", section on 'Conjunctivitis' and "Gonococcal infection in the newborn", section on 'Ophthalmia neonatorum')

•Trauma (see "Conjunctival injury")

●CNS disease:

•Bacterial meningitis (see "Bacterial meningitis in the neonate: Clinical features and diagnosis")

•Viral meningoencephalitis (other than HSV), particularly enterovirus and parechovirus (see "Viral meningitis in children: Clinical features and diagnosis" and "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention", section on 'Neonates')

•CNS insult (eg, anoxia, trauma, or hemorrhage) [60] (see "Clinical features, diagnosis, and treatment of neonatal encephalopathy" and "Germinal matrix and intraventricular hemorrhage (GMH-IVH) in the newborn: Risk factors, clinical features, screening, and diagnosis" and "Child abuse: Evaluation and diagnosis of abusive head trauma in infants and children")

•Neonatal abstinence syndrome (see "Prenatal substance exposure and neonatal abstinence syndrome (NAS): Management and outcomes")

•Inborn errors of metabolism (see "Inborn errors of metabolism: Epidemiology, pathogenesis, and clinical features" and "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management")

•Hypoglycemia (see "Pathogenesis, screening, and diagnosis of neonatal hypoglycemia")

●Disseminated disease:

•Bacterial sepsis (see "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates")

•Adenovirus (see "Pathogenesis, epidemiology, and clinical manifestations of adenovirus infection", section on 'Clinical presentation')

•Enterovirus or parechovirus, particularly during the enteroviral season [35] (see "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention", section on 'Neonates')

•Other neonatal infections, such as cytomegalovirus, toxoplasmosis, syphilis, and rubella (see "Overview of TORCH infections")

•Viral hepatitis (other than HSV), drug-induced hepatitis, or causes of neonatal liver disease (see "Approach to evaluation of cholestasis in neonates and young infants" and "Acute liver failure in children: Etiology and evaluation")

•Viral pneumonia, such as:

-Respiratory syncytial virus (see "Respiratory syncytial virus infection: Clinical features and diagnosis in infants and children")

-Adenovirus (see "Pathogenesis, epidemiology, and clinical manifestations of adenovirus infection")

-Influenza (see "Seasonal influenza in children: Clinical features and diagnosis")

-Parainfluenza (see "Parainfluenza viruses in children")

-Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (see "COVID-19: Clinical manifestations and diagnosis in children")

•Inborn errors of metabolism (see "Inborn errors of metabolism: Epidemiology, pathogenesis, and clinical features" and "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management")

Microbiologic studies (eg, cultures, polymerase chain reaction [PCR] tests) differentiate neonatal HSV from other infectious conditions. Review of the newborn screening results and/or consultation with a geneticist can be helpful to exclude inborn errors of metabolism. Noninfectious dermatologic conditions may have a characteristic clinical course (eg, transient neonatal pustular melanosis, incontinentia pigmenti). However, given increased morbidity and mortality of neonatal HSV disease, and the benefits of early treatment, empiric antiviral therapy for HSV is warranted (after appropriate microbiologic and virologic specimens are obtained) pending definitive diagnosis. (See "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Infectious encephalitis" and "Society guideline links: TORCH infections".)

SUMMARY AND RECOMMENDATIONS

●Epidemiology – Neonatal herpes simplex virus (HSV) infection occurs in approximately 1 in 3200 to 10,000 live births. Neonatal HSV may be acquired in utero (congenital HSV), perinatally (approximately 85 percent of cases), or postnatally (approximately 10 percent of cases). (See 'Epidemiology and transmission' above.)

●Intrauterine infection – Intrauterine HSV is associated with hydrops fetalis and fetal in utero demise. Survivors may exhibit a characteristic triad of skin vesicles or scarring, eye damage, and severe central nervous system (CNS) manifestations including microcephaly, cystic encephalomalacia, or hydranencephaly. (See 'Intrauterine HSV' above.)

●Neonatal HSV – Perinatally and postnatally acquired neonatal HSV may be classified into three main categories for therapeutic and prognostic purposes (table 1):

•Localized SEM disease is characterized by coalescing or clustering vesicular lesions of the skin (picture 5C and picture 5B); excessive tearing, eye pain, conjunctival edema; and/or localized ulcerative lesions of the mouth, palate, and tongue.

•CNS disease, which may be manifested by seizures (focal or generalized), lethargy, irritability, tremors, poor feeding, temperature instability (fever or hypothermia), and full anterior fontanel. (See 'Central nervous system disease' above.)

•Disseminated disease, which involves multiple organs. Neonates with disseminated HSV often present in the first week of life with nonspecific signs and symptoms of neonatal sepsis (eg, temperature dysregulation, apnea, irritability, lethargy, respiratory distress, abdominal distension, hepatomegaly, ascites). The mortality of untreated disseminated neonatal HSV exceeds 80 percent. (See 'Disseminated disease' above.)

●Clinical suspicion – Neonatal HSV infection should be suspected in neonates with any of the following (see 'Clinical suspicion' above):

•Mucocutaneous lesions (picture 5C and picture 5B)

•Abnormal CNS findings (cerebrospinal fluid [CSF] pleocytosis, seizures, focal neurologic signs, abnormal neuroimaging (image 1 and image 2)), or

•Sepsis-like illness (respiratory distress, apnea, abdominal distension, ascites, hepatomegaly, progressive pneumonitis, temperature dysregulation, hepatitis, thrombocytopenia, coagulopathy)

In addition, neonates with perinatal exposure to HSV (eg, maternal active genital lesions) should be monitored for evidence of HSV infection, as summarized in the figure (algorithm 1), and discussed in detail separately.

●Diagnostic evaluation

•Virologic testing – The diagnosis of neonatal HSV infection may be established through isolation of HSV in culture, detection of HSV DNA using qualitative or quantitative polymerase chain reaction (PCR) assays, and/or detection of HSV antigens using direct immunofluorescence assays (DFA). Neonates with suspected HSV infection should have all of the following tests performed (see 'Detection of HSV' above):

-Viral culture or HSV PCR on surface swabs of the conjunctivae, mouth, nasopharynx, and rectum

-Viral culture or HSV PCR (with or without DFA) of swabs/scrapings of any skin and mucous membrane lesions

-CSF HSV PCR

-Whole blood or plasma HSV PCR

-Viral culture or HSV PCR of tracheal aspirate if intubated

•Interpretation – Interpretation of diagnostic testing for HSV in neonates depends upon the clinical circumstances (table 1). Most infected infants have positive viral culture and/or PCR in one or more of the specimens listed above. Similarly, infants with negative viral culture/PCR in all of the above listed specimens are unlikely to be infected with HSV. However, in the setting of highly suggestive clinical, laboratory, or radiologic findings, negative results do not exclude HSV infection. (See 'Interpretation/diagnosis' above.)

•Additional evaluation in confirmed cases – A comprehensive evaluation should be performed in all neonates with confirmed HSV infection to determine the degree of organ involvement. This includes (see 'Additional studies' above):

-Complete blood count, including differential and platelet count

-Liver transaminases, total and direct bilirubin

-Blood urea nitrogen (BUN), creatinine, and urinalysis

-Lumbar puncture (if not already done)

-Ophthalmologic examination

-Neuroimaging

-EEG, if there is other evidence of CNS involvement (eg, seizures, abnormal neurologic examination)

-Chest radiograph if there are pulmonary findings

This evaluation is necessary, even in infants who appear to have isolated SEM disease, because clinical findings may be absent early in the course of CNS and disseminated disease.

•Differential diagnosis – The differential diagnosis of neonatal HSV is broad and includes infectious and noninfectious conditions that are associated with vesicular skin lesions, eye disease, CNS manifestations, and/or systemic illness in neonates. Pending definitive diagnosis, empiric therapy for neonatal HSV may be warranted (after appropriate microbiologic and virologic specimens are obtained). (See 'Differential diagnosis' above and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy'.)