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Infection control measures for prevention of seasonal influenza

Infection control measures for prevention of seasonal influenza
Literature review current through: Jan 2024.
This topic last updated: Jan 26, 2024.

INTRODUCTION — In order to optimally prevent or control influenza outbreaks, it is important to identify cases early and implement multiple infection control measures as soon as possible [1]. Recommendations regarding infection control measures for seasonal influenza infection in health care settings have been provided by the United States Centers for Disease Control and Prevention and will be reviewed here [2].

Health care settings include acute care hospitals, long-term care facilities (eg, nursing homes, skilled nursing facilities), physicians' offices, urgent care centers, outpatient clinics, and home health care [2].

Other prevention strategies for seasonal and avian influenza virus infections are discussed separately. (See "Seasonal influenza in children: Management" and "Seasonal influenza in adults: Role of antiviral prophylaxis for prevention" and "Seasonal influenza in children: Prevention with antiviral drugs" and "Avian influenza: Treatment and prevention".)

TRANSMISSION

Modes of transmission – Influenza virus spreads primarily via person-to-person respiratory transmission, which occurs via close-range contact (ie, within approximately six feet) via large droplets (≥100 microns) and as well as aerosols (<100 microns) [3-5]. When an infected person coughs, sneezes, or talks, virus within respiratory secretions can infect another person if it is inhaled or if it contacts the mucous membranes.

Influenza virus can also be transmitted longer distances through the airborne route (through inhalation of small particle aerosols that remain suspended in the air over time and distance). The extent of this mode of transmission is uncertain [6-8].

Influenza virus transmission can also occur if a person touches a surface contaminated by respiratory secretions and then touches their eyes, nose, or mouth [9].

Incubation period – The typical incubation period is one to four days (average two days) [10,11]. The time between onset of illness among household contacts (known as the serial interval) is three to four days [12].

Viral shedding – In immunocompetent hosts, influenza viral shedding occurs at or just before the onset of symptoms (0 to 24 hours), peaks at 24 to 48 hours of illness, and then rapidly declines, with little or no detectable virus after 5 to 10 days [13-16]. Longer periods of shedding (weeks to months) can occur in adults ≥65 years, individuals with chronic illnesses, persons with obesity and immunocompromised patients [17-20].

INFECTION PREVENTION IN THE HEALTH CARE SETTING

Overview — The United States Centers for Disease Control and Prevention (CDC) has suggested that the following measures be undertaken to prevent the spread of seasonal influenza viruses in health care settings [2]:

Promote and administer the seasonal influenza vaccine to health care personnel (HCP), emergency medical services personnel, and patients, annually. This is the most important measure to prevent seasonal influenza infections. (See "Seasonal influenza vaccination in adults" and "Immunizations for health care providers", section on 'Influenza vaccine'.)

Take steps to minimize potential exposures. (See 'General steps to minimize exposures' below.)

Monitor and manage ill HCP. (See 'Managing health care personnel' below.)

Adhere to standard precautions. (See "Infection prevention: Precautions for preventing transmission of infection", section on 'Standard precautions'.)

Adhere to droplet precautions. (See 'Droplet precautions' below.)

Use caution when performing aerosol-generating procedures. (See 'Aerosol-generating procedures' below.)

Manage visitor access and movement within the facility. (See 'Managing visitor access' below.)

Monitor influenza activity. Health care settings should establish mechanisms and policies by which HCP are alerted promptly about increased influenza activity in the community or if an outbreak occurs within the facility and when collection of clinical specimens for influenza testing may help to inform public health efforts. (See "Seasonal influenza vaccination in adults".)

Implement environmental infection control and engineering controls. A detailed discussion of these measures can be found on the CDC's website.

Train and educate HCP, including those employed by outside employers, on preventing transmission of infectious agents, including influenza virus. Training should be updated periodically and documented.

Key aspects of influenza prevention that should be emphasized include:

Influenza signs, symptoms, complications, and risk factors for complications. HCP should be made aware that, if they have conditions that place them at higher risk of complications, they should inform their health care provider immediately if they become ill with an influenza-like illness so they can receive early treatment if indicated.

The central role of administrative controls such as vaccination, respiratory hygiene and cough etiquette, sick policies, and precautions during aerosol-generating procedures.

Appropriate use of personal protective equipment including respirator fit testing and fit checks.

Use of engineering controls and work practices including infection control procedures to reduce exposure.

Administer antiviral treatment and chemoprophylaxis of patients and health care personnel when appropriate. (See "Seasonal influenza in nonpregnant adults: Treatment" and "Seasonal influenza in adults: Role of antiviral prophylaxis for prevention".)

Attend to the needs of health care personnel at higher risk for complications of influenza (table 1). (See "Seasonal influenza in nonpregnant adults: Treatment".)

Immunization of health care personnel — The care of patients with influenza has led to nosocomial transmission of disease, and infected health care personnel (HCP) have transmitted the virus to patients and other staff. Studies of immunization of HCP against seasonal influenza have demonstrated significant reductions in all-cause patient mortality and influenza-like illnesses among residents of long-term care facilities. (See "Immunizations for health care providers", section on 'Influenza vaccine'.)

The United States Centers for Disease Control and Prevention recommends that all HCP be vaccinated against seasonal influenza virus annually [2]. Strategies used by some institutions to improve vaccination rates among HCP have included providing incentives, providing vaccine at no cost to employees, improving access (eg, offering vaccination at work and during work hours), requiring HCP to sign declination forms to acknowledge that they have been educated about the benefits and risks of vaccination, and mandating influenza vaccination for all HCP without contraindications. Strong organizational leadership and an infrastructure for clear and timely communication and education and for program implementation have been elements of successful programs.

The Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America endorse a policy in which annual influenza vaccination is a condition of employment and/or professional privileges for HCP [21,22]. Some health care facilities that have required mandatory immunization of HCP have attained immunization rates greater than 97 percent [23-25].

General steps to minimize exposures — A range of administrative policies and practices should be used to minimize influenza exposures in health care settings, particularly during periods of increased influenza activity [2]. These include:

Screening and triage of symptomatic patients

When scheduling appointments, instructing patients to inform health care personnel upon arrival if they have symptoms of a respiratory infection and to take appropriate preventive actions (eg, wear a facemask upon entry, follow triage procedure)

During periods of increased influenza activity, taking steps to minimize elective visits (eg, telemedicine appointments or telephone consultations for patients with mild respiratory illnesses who are not at increased risk for complications from influenza to determine if there is a medical need to visit the facility)

Implementation of respiratory hygiene, cough etiquette, and hand hygiene:

Posting visual alerts (eg, signs, posters) in strategic locations (eg, entrance, waiting areas, elevators, cafeterias) with instructions about respiratory hygiene, cough etiquette, and hand hygiene, especially when influenza virus is circulating in the community

Implementing procedures during patient registration that facilitate adherence to appropriate precautions (eg, at the time of check-in, inquire about the presence of symptoms of respiratory infection and, if present, provide instructions)

Providing facemasks to patients with signs and/or symptoms of respiratory infection

Providing alcohol-based hand sanitizers in strategic locations (eg, entrances, waiting rooms, and throughout facilities)

Providing space and encouraging patients with respiratory symptoms to physically distance from others as much as possible

During periods of increased influenza activity, setting up triage stations that facilitate rapid screening of patients for symptoms of influenza and separation from other patients

More details about these measures can be found on the United States Centers for Disease Control and Prevention's website.

Isolation precautions — Precautions to prevent the spread of influenza infections in health care facilities include the use of standard and droplet precautions for the routine care of patients infected with influenza virus.

Influenza viruses are thought to be spread via small particle aerosols and large droplets dispersed after coughing or sneezing [2]. Indirect contact from contaminated surfaces may also occur. (See "Seasonal influenza in adults: Clinical manifestations and diagnosis", section on 'Transmission'.)

Standard precautions — Standard precautions should be used by all health care personnel (HCP) in the health care setting; standard precautions are the foundation for preventing transmission of infectious agents in health care settings [2]. (See "Infection prevention: Precautions for preventing transmission of infection", section on 'Standard precautions'.)

Hand hygiene — Frequent hand hygiene should be performed, including before and after every patient contact, contact with potentially infectious material, and before putting on and after taking off personal protective equipment, including gloves [2]. Hand hygiene can be performed by washing with soap and water or by using alcohol-based hand rubs. If hands are visibly soiled, they should be washed with soap and water. Health care facilities should ensure that supplies for performing hand hygiene are readily available.

In a case-control study of HCP, assignment to units with >75 percent adherence to hand hygiene practices was independently associated with protection from pandemic H1N1 influenza infection (adjusted odds ratio 0.45, 95% CI 0.27-0.89) [26].

Gloves — Gloves should be used for any contact with potentially infectious material, followed by hand hygiene immediately after glove removal [2].

Gowns — HCP should wear a gown for any patient care activity in which contact with blood, respiratory secretions, or other body fluids is anticipated [2]. The gown should be removed and hand hygiene should be performed before leaving the patient's environment.

Droplet precautions — For the prevention of seasonal influenza transmission in health care settings, the United States Centers for Disease Control and Prevention (CDC) recommends the use of droplet precautions for the routine care of patients with suspected or confirmed influenza infection [2].

Droplet precautions include the following practices:

Patients should be placed in a private room or area. When it is not possible to place a patient with influenza in a private room, consult with infection control personnel for input about other placement options (eg, grouping those with influenza together).

HCP should wear a facemask when entering the patient's room. When leaving the patient's room, HCP should remove the facemask, dispose of it, and then perform hand hygiene. Some facilities may choose to provide HCP with alternative equipment, such as respirators and face shields. Studies that have compared facemasks to N95 respirators are discussed below. (See 'Type of respiratory protection' below.)

Hospitalized patients should wear a facemask when they leave their room and should use respiratory hygiene, cough etiquette, and hand hygiene. Information about patients with suspected, probable, or confirmed influenza should be communicated to appropriate personnel before transferring them to other departments in the facility (eg, radiology) or to other facilities. A study of the use of facemasks versus N95 respirators in nine patients with seasonal influenza suggested that both types of mask are equally effective at filtering influenza virus [27].

Droplet precautions are discussed in greater detail separately. (See "Infection prevention: Precautions for preventing transmission of infection", section on 'Droplet precautions'.)

Duration — For immunocompetent inpatients with suspected or confirmed influenza infection, droplet precautions should generally be continued for seven days after illness onset or until 24 hours after resolution of fever and respiratory symptoms, whichever is longer [2].

Isolation precautions may be continued for a longer duration in patients who might shed influenza virus for a longer period, such as young children and severely immunocompromised individuals [2]. (See "Seasonal influenza in adults: Clinical manifestations and diagnosis", section on 'Transmission'.)

Patients should be discharged from the hospital based on their clinical status and should not be kept in the hospital based on the recommended duration of isolation.

Aerosol-generating procedures — Aerosol-generating procedures include endotracheal intubation and extubation, bronchoscopy, sputum induction, cardiopulmonary resuscitation, open suctioning of airways, and autopsies [2]. During aerosol-generating procedures, each HCP should wear an N95 respirator (or an equivalent respirator such as a powered air purifying respirator) as well as adhere to standard precautions, including wearing gloves, a gown, and either a face shield that fully covers the front and sides of the face or goggles. Additional measures should be taken such as conducting procedures in an airborne infection isolation room when feasible and limiting the number of health care personnel present during the procedure. Portable high-efficiency particulate air (HEPA) filtration units can be used to decrease the concentration of contaminants in the air, but they do not eliminate the need for respiratory protection.

Aerosol-generating procedures should only be performed on patients with suspected or confirmed influenza when they are medically necessary and cannot be postponed [2]. Environmental surface cleaning should occur following these procedures.

Type of respiratory protection — As discussed above, the CDC recommends facemasks for the routine care of patients with suspected or confirmed influenza infection and N95 respirators (or an equivalent respirator) for use during aerosol-generating procedures [2]. (See 'Droplet precautions' above and 'Aerosol-generating procedures' above.)

Both facemasks and N95 respirators decrease viral shedding into the environment and may also reduce hand-to-mouth inoculation of virus [28]. N95 respirators fit tightly and filter out small particles. However, the optimal use of N95 respirators requires fit testing, training, and medical clearance. Furthermore, it is not clear that N95 respirators are more efficacious than facemasks in preventing influenza [29].

During the 2009 to 2010 H1N1 influenza pandemic, the CDC and the Institute of Medicine recommended the use of fit-tested N95 respirators for health care personnel in close contact with patients with suspected or confirmed pandemic H1N1 influenza A infection [30-32]. However, some facilities experienced shortages of N95 respirators. Additionally, there was controversy about the optimal mode of respiratory protection.

The efficacy of facemask use was addressed in a trial involving 1437 young adults living in university residence halls in which significant reductions in influenza-like illness were observed among those randomly assigned to a facemask and hand hygiene group compared with those assigned to no intervention [33]. All participants, including those in the control group, were also instructed on the importance of handwashing.

Most but not all studies have not shown a difference in efficacy between facemasks and N95 respirators for preventing influenza infections or other respiratory virus infections among HCP [29,34-36]. A 2017 meta-analysis of randomized trials indicated a protective effect of facemasks and N95 respirators in HCP against clinical respiratory illness (risk ratio [RR] 0.59, 95% CI 0.46-0.77) and influenza-like illness (RR 0.34, 95% CI 0.14-0.82) [35]. Compared with facemasks, N95 respirators conferred greater protection against clinical respiratory illness (RR 0.47, 95% CI 0.36-0.62) and laboratory-confirmed bacterial infections (RR 0.46, 95% CI 0.34-0.62) but not against viral infections or influenza-like illness.

In a subsequent randomized trial that included 2371 HCP from 137 outpatient sites at seven United States medical centers, pairs of outpatient sites within each center were matched and randomly assigned to have their HCP use N95 respirators or facemasks when coming within 6 feet of patients with respiratory illness during the 12-week period of peak viral respiratory illness over four influenza seasons [36]. There were a similar number of laboratory-confirmed influenza infection events in the N95 respirator and facemask groups (207 versus 193 events; adjusted odds ratio 1.18, 95% CI 0.95-1.45). There were also no significant differences between the groups in the incidence of acute respiratory illness events, laboratory-detected respiratory infections, laboratory-confirmed respiratory illness events, or influenza-like illness events.

For respiratory protection to be effective, it is crucial to achieve a proper fit. In a study that used coughing and breathing manikins, a tightly sealed facemask blocked entry of 94.8 percent of infectious influenza virus from entering the mouth and a tightly sealed N95 respirator blocked 99.6 percent of infectious virus [6]. By contrast, a poorly fitting facemask blocked entry of 56.6 percent of infectious virus, and a poorly fitting N95 respirator blocked 66.5 percent of infectious virus.

The use of facemasks in the household setting is discussed separately. (See "Seasonal influenza in nonpregnant adults: Treatment", section on 'Infection control and returning to work/school'.)

Managing visitor access — Visitor access to patients in isolation for influenza should generally be limited to individuals who are necessary for the patient's care and well-being [2]. When visits are planned, the following measures should be taken:

Visitors should be screened for symptoms of acute respiratory illness before entering the facility.

Facilities should provide instruction before visitors enter the patient's room on hand hygiene, limiting surfaces touches, and use of personal protective equipment.

Visitors should use respiratory hygiene and cough etiquette.

Visitors should not be present for aerosol-generating procedures.

Visitors should be instructed to limit their movement within the facility.

Visitors should be vaccinated against influenza by their health care provider.

Health care facilities should develop visitor restriction policies for individuals with respiratory symptoms related to the location of the patient being visited (eg, oncology units). Specific circumstances requiring exemption from the restriction (eg, end-of-life situations) should also be considered. (See 'General steps to minimize exposures' above.)

Managing health care personnel

Chemoprophylaxis — Recommendations for antiviral prophylaxis following exposure to individuals with influenza infection are reviewed separately. (See "Seasonal influenza in adults: Role of antiviral prophylaxis for prevention".)

Ill health care personnel — Health care personnel (HCP) with fever and respiratory symptoms should [2]:

Not report to work or, if already at work, stop patient-care activities, wear a facemask, and promptly notify their supervisor and infection control or occupational health before swiftly leaving work.

Be reminded that adherence to respiratory hygiene, cough etiquette, and hand hygiene after returning to work is important.

If symptoms such as coughing and sneezing are still present, wear a facemask after returning to work.

Be excluded from work until at least 24 hours after fever has abated (without the use of antipyretics).

Be evaluated by occupational health before returning to work if respiratory symptoms remain present.

Be considered for temporary reassignment or exclusion from work for seven days after symptom onset or until resolution of symptoms, whichever is longer, if returning to care for patients in a protected environment, such as hematopoietic cell transplant recipients.

Fever may be absent [37]; therefore, it may be difficult to differentiate influenza from other causes of respiratory symptoms, especially early in the course of illness. HCP with isolated fever should leave work or stay home.

Additional recommendations for the evaluation and management of ill HCP and the development of sick leave policies can be found on the United States Centers for Disease Control and Prevention's website.

The treatment of influenza is discussed separately. (See "Seasonal influenza in nonpregnant adults: Treatment".)

HCP at increased risk for complications — It is particularly important that health care personnel (HCP) who are at increased risk for influenza complications be vaccinated annually against influenza (table 1); such individuals should also be treated early if influenza infection develops [2]. (See "Seasonal influenza in nonpregnant adults: Treatment".)

Work accommodations to avoid potentially high-risk exposures to patients with suspected or confirmed influenza (eg, participation in aerosol-generating procedures) may be considered in some settings, such as HCP with severe underlying diseases [2]. (See "Seasonal influenza in nonpregnant adults: Treatment".)

Monitoring influenza activity — Health care facilities should implement mechanisms and policies by which health care personnel (HCP) are alerted promptly about increased influenza activity in the community or if an outbreak occurs within the facility and when collection of clinical specimens for influenza virus testing may help to inform public health efforts to control transmission [2]. Close communication and collaboration with local and state health authorities is recommended. Policies should include designation of specific persons within the health care facility who are responsible for communication with public health officials and dissemination of information to HCP.

Antiviral treatment and prophylaxis — Some studies have suggested that early antiviral treatment of influenza-infected persons reduces transmission via diminished shedding [38], although the magnitude of effect is uncertain [38-40]. Issues for related to antiviral prophylaxis for prevention of infection following exposure to individuals with influenza are reviewed separately. (See "Seasonal influenza in adults: Role of antiviral prophylaxis for prevention".)

INFECTION PREVENTION IN THE OUTPATIENT SETTING — Home-based infection control measures home may be beneficial [41,42]. One cluster-randomized trial found that use of hand hygiene and face masks reduced household transmission when implemented within 36 hours of symptom onset in the index patient (adjusted odds ratio 0.33, 95% CI 0.13-0.87) [41].

Issues for related to antiviral prophylaxis for prevention of infection following exposure to individuals with influenza are reviewed separately. (See "Seasonal influenza in adults: Role of antiviral prophylaxis for prevention".)

RETURNING TO WORK/SCHOOL — Individuals with influenza who are managed as outpatients should remain home from work, school, and other public places until at least 24 hours after defervescence (without use of antipyretics) [43].

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: Infection control".)

SUMMARY AND RECOMMENDATIONS

In order to optimally prevent or control influenza outbreaks, it is important to identify cases early and implement multiple infection control measures as soon as possible. Recommendations regarding infection control measures for seasonal influenza infection in health care settings have been provided by the United States Centers for Disease Control and Prevention (CDC). (See 'Introduction' above and 'Overview' above.)

Influenza virus spreads primarily via person-to-person respiratory transmission, which occurs via close-range contact (ie, within approximately six feet) via large droplets (≥100 microns) and as well as aerosols (<100 microns). The typical incubation period is one to four days (average two days). The time between onset of illness among household contacts (known as the serial interval) is three to four days. (See 'Transmission' above.)

All health care personnel (HCP) should be vaccinated against seasonal influenza annually. The Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America endorse a policy in which annual influenza vaccination is a condition of employment and/or professional privileges for HCP. (See 'Immunization of health care personnel' above.)

It is particularly important that HCP who are at increased risk for influenza complications be vaccinated annually against influenza (table 1); such individuals should also be treated early if influenza infection develops. (See 'HCP at increased risk for complications' above.)

A range of administrative policies and practices should be used to minimize influenza exposures in health care settings, particularly during periods of increased influenza activity. (See 'General steps to minimize exposures' above.)

Precautions to prevent the spread of influenza infections in health care facilities include the use of standard and droplet precautions when caring for patients infected with influenza virus. Facemasks should be used for the routine care of patients with suspected or confirmed influenza infection. Some facilities may make N95 respirators (or equivalent) available for routine care of patients with influenza infection. Respirators should be worn during aerosol-generating procedures. (See 'Isolation precautions' above.)

Visitor access to patients in isolation for influenza should generally be limited to individuals who are necessary for the patient's care and well-being. (See 'Managing visitor access' above.)

HCP with fever and respiratory symptoms should not report to work or, if already at work, should stop patient care activities, wear a facemask, promptly notify their supervisor and infection control, and leave work. (See 'Ill health care personnel' above.)

Individuals with influenza should remain home from work, school, and other public places until at least 24 hours after defervescence (without use of antipyretics). (See 'Returning to work/school' above.)

Additional details about infection control measures to prevent influenza in health care settings can be found on the CDC's website.

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Anna R Thorner, MD, who contributed to an earlier version of this topic review.

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Topic 6999 Version 28.0

References

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