ACIP guidelines cite risk of nosocomial cases
Infection control measures recommended
New guidelines on the prevention of varicella zoster virus (VZV) infections by the Atlanta-based Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices underscore the following points pertinent to health care workers and their patients.1
* Epidemiology.
VZV can be transmitted from person to person by direct contact, droplet, aerosol from vesicular fluid of skin lesions, and secretions from the respiratory tract. The virus enters the host through the upper-respiratory tract. The average incubation period for varicella is 14 to 16 days; however, this period can range from 10 to 21 days. The period of contagiousness of infected people is estimated to begin 1 to 2 days before the onset of rash and end when all lesions are crusted, which is usually 4 to 5 days after the onset of a rash.
Epidemiologic and serologic studies confirm that more than 90% of adults are immune to VZV. Otherwise healthy children and adolescents under 15 years old comprise some 80% of the estimated 9,300 annual varicella-related hospitalizations. The most common complications of varicella which result in hospitalization are bacterial infections of skin lesions, pneumonia, dehydration, encephalitis, and hepatitis.
* Types of exposure.
Substantial exposure for hospital contacts consists of sharing the same hospital room with an infectious patient or prolonged, direct, face-to-face contact with an infectious person by health care workers. Brief contacts with an infectious person (e.g., contact with X-ray technicians or housekeeping personnel) are less likely to result in VZV transmission than are more prolonged contacts. Persons with continuous exposure to household members who have varicella are at greatest risk for infection.
* Nosocomial Transmission.
Sources of nosocomial exposure have included patients, hospital staff, and visitors (e.g., the children of hospital employees) who are infected with varicella or herpes zoster. In hospitals, airborne transmission of VZV has been demonstrated when varicella has occurred in susceptible persons who have had no direct contact with the index case patient. Although severe varicella disease and complications can occur in all susceptible people, patients at higher risk include infants born to susceptible mothers, and immunocompromised persons of all ages.
Strategies for managing clusters of VZV infection in hospitals include isolating patients who have varicella and susceptible patients who have been exposed to the virus; controlling air flow; using rapid serologic testing; furloughing or screening exposed, susceptible personnel daily for skin lesions, fever, and systemic symptoms; and temporarily reassigning susceptible personnel to locations remote from patient-care areas. Appropriate isolation of hospitalized patients who have confirmed or suspected VZV infection can reduce the risk for transmission to personnel.2 Only personnel who are immune to varicella should care for these patients. If susceptible personnel are exposed to varicella, they are potentially infective 10 to 21 days after exposure and are too often furloughed, usually at substantial cost. The use of VZIG immune globulin following exposure can be costly, does not necessarily prevent varicella, and may prolong the incubation period by one week or more thus extending the time during which personnel should not work in patient areas.
* Health care workers.
All susceptible health care workers should ensure they are immune to varicella. In health care institutions, serologic screening of personnel who have a negative or uncertain history of varicella is likely to be cost-effective. Routine testing for varicella immunity after two doses of vaccine is not necessary for the management of vaccinated health care workers who may be exposed to varicella, because 99% of persons are seropositive after the second dose. Seroconversion, however, does not always result in full protection against disease. Testing vaccinees for seropositivity immediately after exposure to VZV is a potentially effective strategy for identifying persons who remain at risk for varicella. Prompt serologic results may be obtained using the latex agglutination test.
Varicella is unlikely to develop in persons who have detectable antibody. Persons who remain susceptible may be furloughed. Alternatively, persons can be monitored daily to determine clinical status and then furloughed at the onset of manifestations of varicella. Institutional guidelines are needed for the management of exposed vaccinees who do not have detectable antibody and for persons who develop clinical varicella. Vaccination should be considered for unvaccinated health care workers who are exposed to varicella and whose immunity is not documented. However, because the protective effects of post-exposure vaccination are unknown, persons vaccinated after an exposure should be managed in the manner recommended for unvaccinated persons.
Reference
1. Centers for Disease Control and Prevention. Prevention of varicella: Recommendations of the Advisory Committee on Immunization Practices. MMWR 1996; 45(No. RR-11):1-36.
2. Centers for Disease Control. Guidelines for isolation precautions in hospitals. Infect Control Hosp Epidemiol 1996; 17:54-80. *
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