Before considering the infection control strategies recommended during the current H1N1 influenza pandemic, it is useful to review the transmission characteristics of influenza viruses—including H1N1—that form the basis for these strategies:

•Spread of infection tends to occur via large-droplet transmission.
•Once expelled into the air, large droplets tend to travel less than 6 feet before they fall to the ground.
•Viral particles may persist on nonporous surfaces and may be transferable to hands for variable periods of time.
•Aerosolization of the virus may occur during certain procedures—eg, bronchoscopy, intubation.
•Overall, airborne transmission (by generation of small-droplet nuclei)—such as is seen in tuberculosis, varicella, and measles—is not considered a major route of transmission for influenza viruses; more research is needed to determine the significance of airborne transmission over short distances in the health care setting.
•People tend to sneeze or cough into their hands and may transmit the virus to others if, in the interim, they do not practice effective hand hygiene to reduce the viral burden on their hands.
•Soap and water, as well as alcohol-based hand rubs, are very effective, especially when they are used appropriately (with soap and water, cleaning all surfaces of the hands and for sufficient time—30 seconds minimum; with gels, rubbing until the hands are dry). It is prudent for health care workers to practice hand hygiene as often as possible throughout the day, and certainly before every patient encounter. Several studies support this best practice.^1,2
•Infected persons may be contagious from 1 day before the onset of symptoms until the time when symptoms resolve.

PRECAUTIONS TO TAKE IN HEALTH CARE SETTINGS

Current guidelines seem to recommend an overall more cautious approach with H1N1 than with seasonal influenza, primarily because it is too early to tell definitively whether novel H1N1 influenza viruses possess the same transmission characteristics as seasonal influenza. Measures that are recommended in health care settings include Standard and Contact Precautions (gown, gloves, eye protection, and masks). The specifics of the CDC guidelines for control of H1N1 infection, which are continuously updated, are available at http://www.cdc.gov/h1n1flu/guidelines_infection_ control.htm.

Masks and eye protection. According to the CDC, the preferred mask in the health care setting is a fit-tested, disposable N-95 respirator, which should be donned on entering a room. N95 respirators filter out at least 95% of particles (measuring 0.3 mm or larger), including those slightly smaller than the influenza virus itself. Even though surgical masks are considered the appropriate respiratory device to be worn on the face in the context of seasonal influenza (with H1N1 influenza presumed to have a similar transmission pattern), the N-95 mask is recommended for use in health care settings in the current outbreak largely because the extent of airborne transmission of H1N1 is unknown and more research needs to be done. This approach is supported by the CDC and a recent Institute of Medicine report.³ However, complete consensus regarding which type of respiratory device is recommended (surgical mask or N95 respirator) is still lacking, with the guidelines of other groups (such as the World Health Organization, Society for Healthcare Epidemiology of America, and Infectious Disease Society of America) being somewhat less stringent concerning respirators.^4,5

N95 devices are, nonetheless, clearly recommended in settings in which aerosol-generating procedures are being performed. N-95 masks are disposable but can be reused repeatedly over 12 hours—‘however, only if all of the following criteria are met:

•Only 1 health care worker (HCW) uses the mask for only 1 patient (not for several).
•The mask is stored neatly in a clean, dry area if doffed during the period of use.
•The mask is kept free of dirt and humidity.

Patients who are likely to or definitely have H1N1 influenza should be asked to wear a surgical mask when they are coughing or sneezing and around other people. This is especially important in crowded areas, such as waiting rooms, and during clinic or hospital transport. Meticulous attention must be paid to patient flow in waiting rooms, clinic rooms, and procedure rooms or suites. Office staff in ambulatory care settings should also be afforded protection.

Surgical masks should be routinely used to protect patients and health care workers and prevent
droplet transmission in the context of clinical care. If "triage rooms“ or de facto "isolation rooms“ can be set up, the use of N-95 respirators may be integrated into clinical care. Guidance is available to help clinicians with infection control issues that arise in this setting.⁶ A tabular summary of facemask and respirator use is available on the CDC Web site (http://www.cdc.gov/h1n1flu/ masks.htm); it provides interim recommendations for non-ill persons in the home, community, and occupational settings.

Eye protection devices (goggles or face shields) should be used to protect workers from droplet transmission, especially in the context of splashing, aerosol-generating procedures.