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Hospitalizations and Deaths Hospitalization rates during influenza season are substantially increased for persons aged >65 years. One retrospective analysis based on data from medical records collected during 1996-2000 estimated that the risk during influenza season among persons aged >65 years with underlying conditions that put them at risk for influenza-related complications (i.e., one of more of the conditions listed as indications for vaccination) was approximately 56 influenza-associated hospitalizations per 10,000 persons, compared with approximately 19 per 10,000 healthy elderly persons. Persons aged 50-64 years with underlying medical conditions also were at substantially increased risk for hospitalizations during influenza season, compared with healthy adults aged 50-64 years. No increased risk for influenza-associated hospitalizations was demonstrated among healthy adults aged 50-64 years or among those aged 19-49 years, regardless of underlying medical conditions (52). During 1976-2001, an estimated yearly average of 32,651 (90%) influenza-related deaths occurred among adults aged >65 years (1). Risk for influenza-associated death was highest among the oldest elderly, with persons aged >85 years 16 times more likely to die from an influenza-associated illness than persons aged 65-69 years (1). Limited information is available regarding the frequency and severity of influenza illness among persons with human immunodeficiency virus (HIV) infection (64,65). However, a retrospective study of young and middle-aged women enrolled in Tennessee's Medicaid program determined that the attributable risk for cardiopulmonary hospitalizations among women with HIV infection was higher during influenza seasons than it was either before or after influenza was circulating. The risk for hospitalization was higher for HIV-infected women than it was for women with other underlying medical conditions (66). Another study estimated that the risk for influenza-related death was 94-146 deaths per 100,000 persons with acquired immunodeficiency syndrome (AIDS), compared with 0.9-1.0 deaths per 100,000 persons aged 25-54 years and 64-70 deaths per 100,000 persons aged >65 years (67). Influenza symptoms might be prolonged and the risk for complications from influenza increased for certain HIV-infected persons (68-70). Influenza-associated excess deaths among pregnant women were reported during the pandemics of 1918-1919 and 1957-1958 (71-74). Case reports and several epidemiologic studies also indicate that pregnancy can increase the risk for serious medical complications of influenza (75-80). The majority of recent studies that have attempted to assess the effect of influenza on pregnant women have measured changes in excess hospitalizations for respiratory illness during influenza season but not laboratory-confirmed influenza hospitalizations. Pregnant women have an increased number of medical visits for respiratory illnesses during influenza season compared with nonpregnant women (81). Hospitalized pregnant women with respiratory illness during influenza season have increased lengths of stay compared with hospitalized pregnant women without respiratory illness. For example, rates of hospitalization for respiratory illness were twice as common during influenza season (82). A retrospective cohort study of approximately 134,000 pregnant women conducted in Nova Scotia during 1990-2002 compared medical record data for pregnant women to data from the same women during the year before pregnancy. Among pregnant women, 0.4% were hospitalized and 25% visited a clinician during pregnancy for a respiratory illness. The rate of third-trimester hospital admissions during the influenza season was five times higher than the rate during the influenza season in the year before pregnancy and more than twice as high as the rate during the noninfluenza season. An excess of 1,210 hospital admissions in the third trimester per 100,000 pregnant women with comorbidities and 68 admissions per 100,000 women without comorbidities was reported (83). In one study, pregnant women with respiratory hospitalizations did not have an increase in adverse perinatal outcomes or delivery complications (84), but they did have an increase in delivery complications in another study (82). However, infants born to women with laboratory-confirmed influenza during pregnancy do not have higher rates of low birth weight, congenital abnormalities, or low Apgar scores compared with infants born to uninfected women (79,85).. |