Viruses are important causes of nosocomial infection, but apart from specific situations such as the follow-up of known or suspected exposure to blood-borne viruses or the investigation of outbreaks, there are usually insufficient data to allow the monitoring of trends in incidence. When routine monitoring has been carried out, 5% of all nosocomial infections have been attributed to viruses, and this figure is likely to be an underestimate. Pediatric units and wards with elderly patients are particularly prone to seasonal introductions and nosocomial spread of viral infections; in one study, 32% of pediatric nosocomial infection were attributed to viruses, of which respiratory syncytial virus (RSV) was the most common.
The most important defense against nosocomial transmission of viruses and other infectious agents is detailed and continuing education of staff and strict adherence to infection control policies. The doctor, nurse, or medical student, who may have rapid contact with a succession of patients of varying degrees of vulnerability, provides an excellent potential vector for virus carriage and transmission. All involved in patient care should be aware of the potential dangers to patients of continuing to work while suffering from a respiratory infection, cold sores, or other viral disease. The mundane but critically important role of adequate handwashing after examining every patient must be emphasized, as must the potential risks to the workers, and to their patients, of breaks in hygienic practice such as eating, drinking, smoking, applying cosmetics, or inserting contact lenses in clinical or laboratory areas and from touching their mouth or eyes during the course of their work.
In an outbreak situation, whether the origin is within the hospital or in the community, it may be necessary to consider cohort isolation. This normally involves separately accommodating groups of infected and apparently uninfected individuals. It may also involve a third group of individuals who have been exposed and are at risk of developing the infection. If one of the exposed or the “uninfected” group develops the disease, they are immediately moved to the infected cohort.
In an outbreak situation, whether the origin is within the hospital or in the community, it may be necessary to consider cohort isolation. This normally involves separately accommodating groups of infected and apparently uninfected individuals. It may also involve a third group of individuals who have been exposed and are at risk of developing the infection. If one of the exposed or the “uninfected” group develops the disease, they are immediately moved to the infected cohort.
Respiratory viruses (RSV, influenza viruses A and B, parainfluenza viruses 1 to 3, rhinoviruses, and adenoviruses) are increasingly recognized as significant pathogens; given the relative ease with which they spread and their relatively short incubation times (usually between 1 and 8 days), these viruses can result in significant nosocomial problems. Transmission occurs via spread of either small (median diameter, <5 μm) or large droplets. Typically, small droplets containing infectious virus particles are generated by coughing, sneezing, or talking and are readily transmitted over considerable distances. This is in contrast to large droplets, for which transmission usually only follows close person-to-person contact and results from direct inoculation of virus-laden droplets onto the mucous membranes (e.g., eye and nose) of the susceptible host. Autoinoculation can also lead to infection and results from the transfer of virus from hands to mucous membranes. The prevention of spread of respiratory virus infections within a hospital or other institution (e.g., old people's home or psychiatric home) depends on the early diagnosis of the infection.
Respiratory Syncytial Virus
RSV is a major cause of morbidity in infants and young children and has been reported to be responsible for approximately 45% of all hospital admissions for acute respiratory disease in those under the age of 2 years. Bronchiolitis and pneumonia are the most common manifestations in young children, with most children having been exposed by 5 years of age. However, immunity to reinfection is not permanent, with older children and immunocompetent adults developing recurrent episodes of mild upper respiratory tract infections throughout life. RSV is seasonal, occurring in the winter months (usually November to February or March) in temperate climates, and may result from the cocirculation of two antigenically distinct types of the virus within the community.
RSV is spread by close contact with infectious respiratory secretions inoculated into the eyes or nose either via large droplets or from fomites. Infected infants shed large amounts of virus in their respiratory secretions, usually for about 7 days (range, 1 to 21 days), and it is likely that transmission occurs via the ungloved or unwashed hands of health care workers or relatives. Contamination of the environment is another important source of nosocomial infections. Hall et al. have shown that RSV can persist on skin and porous surfaces such as gowns and paper tissues for up to 30 min and for up to 6 h on nonporous surfaces, e.g., gloves and countertops. Subsequent transfer and persistence of virus from these surfaces on skin were also demonstrated, supporting the idea that contaminated hands are important in the nosocomial transmission of this infection. Small-droplet spread is much less common but can occur when the source and recipient are in close contact (within 1 m), e.g., coughing, sneezing, or aspiration of infected secretions. Cross-infection on pediatric wards is a common problem, with over 40% of children becoming infected if hospitalized during the winter months for more than 7 days, and each year approximately 50% of pediatric staff acquire the infection.
Control of spread. Numerous studies have been conducted to determine the best strategy to prevent the nosocomial transmission of RSV. There is general agreement that rapid laboratory diagnosis (direct antigen detection in nasopharyngeal cells), the wearing of aprons or gowns and gloves (for close contact with infected infants), and source isolation (or cohorting of infected patients) are essential. Whereas efficient handwashing, even with proprietary soap preparations, is extremely effective in reducing transmission, many studies have shown that handwashing practices even in intensive care units are suboptimal. Repeated handwashing may result in chapped, irritated skin, and this may deter the practice. The need for masks is less clear. There is some evidence that their use in conjunction with other infection control procedures may reduce nosocomial transmissions to high-risk patients.
To interrupt nosocomial transmission, it is essential that all possible cases of hospital acquired infection be identified early and that the infection control team be informed so that the appropriate procedures are implemented. Jones et al. partly attributed an outbreak in a BMT unit to a delay in informing the infection control team.
Influenza Viruses A and B
Influenza A and B virus infections are characterized by the sudden onset of fever, coryza, sore throat, headache, and profound myalgia. The symptoms typically last about 7 days in the immunocompetent host, with some patients developing a protracted cough. The period of infectivity is taken as either 7 days from the onset of symptoms or until symptoms cease, whichever is the longest. During major epidemics, severe illness and death from primary viral or secondary bacterial pneumonia can occur, usually in the elderly, those with underlying disease (cardiac, pulmonary, renal, or metabolic), and the immunocompromised. In hospitalized BMT patients, influenza is often complicated by pneumonia, with an associated mortality of 50%. Unlike RSV, however, only half of the pneumonias are viral in origin, the others being secondary to bacterial or fungal superinfections.
Influenza virus infections occur mainly in the winter months and, depending on the level of immunity in the community and the nature of the main circulating viruses, may result in sporadic infections or epidemics. Pandemics result from the genetic reassortment (antigenic shift) in influenza A viruses and, as there is little or no immunity in the community after such an event, usually affect a large proportion of the population.
Control of spread.Measures to control the nosocomial spread of influenza virus infections are based on those outlined for RSV, with particular emphasis on droplet precautions, including the wearing of masks.
Rotavirus
Rotaviruses are recognized as an important cause of nosocomial infection, particularly in infants and children under the age of 5 years and in the elderly. They may also cause nosocomial gastroenteritis in the immunocompromised. In outbreaks in hospital nurseries, 33 to 70% of infants have been shown to shed rotavirus in the stool, and 8 to 28% of the shedders have clinical symptoms. Rotaviruses have been found to account for nearly 50% of all cases of nosocomially acquired infectious gastroenteritis in pediatric patients.
Rotaviruses have been identified as the cause of diarrhea outbreaks in elderly hospitalized patients. Although adults with normal immune systems rarely have symptomatic infection, Yolken et al. reported rotaviruses as the causative agent in 9 of 31 patients with infectious diarrhea in a BMT unit.
Control of spread.The principle for control of rotaviruses, as with other enteric viral infections, is the institution of single-room or cohort isolation with enteric precautions. Although sodium hypochlorite is used for general disinfection, 70 or 95% alcohol handrubs are recommended as an adjunct to handwashing to prevent patient-to-patient transmission.
Enteroviruses
The enteroviruses are a genus of the Picornavirus family and include coxsackieviruses A and B, echoviruses, polioviruses, and enteroviruses 68 to 71. They are transmitted by the fecal-oral route, but coxsackievirus A21 has been reported to spread by droplet transmission, and other enteroviruses are probably spread by this route. Virus shedding in the oropharynx and in feces may continue for at least 1 month after infection.
