As another flu season approaches, the Advisory Committee on Immunization Practices (ACIP) has published a comprehensive guide to preventing and controlling outbreaks of the illness. The report notes that in the United States, annual epidemics of influenza occur typically during the late fall and winter seasons, with rates of infection highest in children. • Children and adolescents receiving long-term aspirin therapy who therefore might be at risk for developing Reye syndrome after influenza virus infection; • Adults and children who have chronic pulmonary or metabolic disorders (including asthma and diabetes); • Adults and children who have immunosuppression caused by medication or by HIV; • Adults and children who have any condition (e.g., cognitive dysfunction, spinal and cord injuries, seizure disorders, or other neuromuscular disorders) that can compromise respiratory function; • Health care personnel; • Healthy household contacts, including children, and caregivers of children up to five years of age, with particular emphasis on vaccinating contacts of children under six months of age. The ACIP offers a refresher on the background and epidemiology of influenza. The report notes that there are two types of viruses that cause human infection, A and B, subtypes of which circulate globally. Annual vaccinations are required because new influenza variants regularly emerge, as the result of mutations that occur during viral replication As for the epidemiology--influenza spreads from person to person primarily through “large-particle respiratory droplet transmission” as when an infected person coughs or sneezes near a susceptible person. Droplets do not remain suspended in air and usually travel only a short distance. It’s also possible to come into contact with droplets on a contaminated surface. The typical incubation period for the flu is one to four days, with an average of two days. Adults can be infectious from the day before symptoms begin and through approximately five days after illness onset. Young children also might shed virus several days before illness onset, and children can be infectious for as much as ten days after onset of symptoms. The clinical signs of influenza are well known to most people—fever, headache, malaise, nonproductive cough, sore throat, and a runny nose, for example. But there are considerable variations in symptoms, and studies of adults and children who were thought to have the flu have shown that laboratory confirmation is needed in many cases. That could be important, because an attack of influenza can result in hospitalization or death. For children, rates of hospitalization are higher among young children than older children; and while influenza-related deaths are uncommon among children, they represent a substantial proportion of all flu-associated deaths and often occur in children who have no known risk factors for complications. Prevention Strategies Stressing that annual vaccination is far and away the best way to avoid getting the flu, the report also mentions some other prevention strategies, including two that are reasonable and inexpensive—frequent handwashing and “improved respiratory hygiene,” which might include teaching children to cough or sneeze into tissues. Antiviral drugs used to treat influenza are no substitute for vaccination, and it’s not clear if community-level interventions such as closing schools do much to control viral transmission during typical flu seasons, though school closings are always mentioned as a first line of defense against any widespread influenza epidemics. Comprehensive information about annual influenza season is available as a Recommendation and Report from the Advisory Committee on Immunization Practices, July 13, 2007, at www.cdc.gov/mmwr.
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