Managed Care - October 2008 - (Page IS4) 10 million to 60 million cases of acute influenza each year which usually lasts about 3 months. This spike is a bell in the United States, leading to as many as 25 million ofcurve that reflects the period of rapid spread and peakfice visits, 200,000 hospitalizations, and 36,000 deaths ing of the epidemic, and the subsequent mounting of an (CDC 2008b, Couch 2000, U.S. Census Bureau 2008). immune response that mitigates the illness in the indiVirus transmission. Influenza is transmitted primavidual patient within 2 to 3 days (CDC 2008c). There is rily via airborne respiratory secretions released in the often a second surge of influenza infection caused by the event of a cough or a sneeze. It is believed that the virus B virus several weeks later due to lower and slower rates settles in the host trachea and lungs and is absorbed of transmission of influenza B, although in the into tissue by endocytosis. The virus replicates in the 2007–2008 U.S. influenza season, A and B illnesses aplower airway, with onset of cough and fever within 1 to peared to circulate simultaneously. Similarly, the peak 2 days of infection (Moser 1979). The highest mortality month of illness generally falls in January or February, related to influenza occurs among elderly patients over but has been reported as early as November and as late age 65 and among patients with chronic conditions that as April (CDC 2008c). are risk factors for influenza complications. An aggressive effort to mitigate the disease with mediDiagnosis trends cation and vaccination has long existed in these high-risk The clinical diagnosis of influenza is moderately relipopulations. Today, however, it is becoming increasingly able in the event of a flu epidemic; in a community with clear that children, in fact, bear the greater burden of inwidespread flu, the presence of cough and the acute fection. Although death rates are lower in this group, onset of fever indicates influenza with 70 percent specichildren experience the highest rates of sero-positive inficity (Hayden 2004). Without prevalent flu, however, it fection and are hospitalized for flu symptoms in much is much harder to diagnose influenza, because these comhigher numbers than the elderly (CDC 2001a). One study mon symptoms can suggest a wide range of alternative estimated a rate of 1,000 children per 100,000 population disorders. versus 150 elderly per 100,000 population (Neuzil 2000). Laboratory culture is the standard method used to Children also are responsible for most of the virus establish the presence of influenza infection, but it is a transmission throughout the community. Glezen (1997) time-consuming procedure. Polymerase chain reaction followed patterns of influenza in 145 Houston-area fam(PCR) tests are equivalent to, or better than, laboratory ilies and reported an overall infection rate of 32.8 per 100 culture, offering greater sensitivity. PCR utilizes nasophapatient-years. The highest rate of 47.7 per 100 patientryngeal aspirate or nose/throat swab to detect influenza years was observed in children aged 6 to 10 (Figure 2). Rates of infection Rates of influenza and influenza-related illnesses are highest in decreased progressively in each adchildren aged 6 to 10 and lowest in the adult population vancing age group, and actual rates 50 of infection were lowest among Influenza virus infection adults older than age 25. Acute respiratory infection Thus, what begins as a disease of Lower respiratory infection 40 children, acquired and circulated in the closed community of school, is now believed to pass on secondar30 ily to adults, first within the home, then into the local environment (neighborhoods and regular con20 tacts), and ultimately, reaching the greater community at large. Transmission from child to child in the 10 school setting expands this infected universe by multiples (Elveback 1976). 0 Patterns of epidemics. The re≥35 <2 2–5 6–10 11–17 18–24 25–34 sultant disease epidemics take on Age (years) fairly predictable patterns of proFIGURE 2 Age-specific annual influenza infection rates, Houston family study, gression. After a gradual increase in 1976–1984 the proportion of patients with isoSource: Glezen 1997 lates of type A influenza, there is a rapid spike in infection prevalence, Rate per 100 persons 4 MANAGED CARE / SUPPLEMENT
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