Pulmonary complications of interpandemic influenza A in hospitalized adults

Background. To define the pulmonary complications of influenza during the current interpandemic period, we reviewed clinical, laboratory, and radiographic data from 193 adults (>= 18 years old) (1999-2003) who were hospitalized with influenza A during 4 winters. Results. The mean age was 75 years, 8% had documented bacterial infection, 15% required intensive care unit treatment, and 6% died. Chest radiograph (CXR) findings were classified as showing acute disease (AD; n = 101) or no AD (NAD; n = 92). Most CXR findings were subtle in nature. Subjects with AD were more likely to have >= 1 cardiac diagnosis (odds ratio [OR], 2.2 [95% confidence interval {CI}, 1.2-4.1]), to have rales on examination (OR, 1.9 [95% CI, 1.0-3.7]), to be symptomatic for > 3 days ( OR, 2.2 [ 95% CI, 1.2-4.1]), and to be less likely to wheeze (OR, 0.37 [95% CI, 0.20-0.70]). Total and neutralizing anti-influenza antibody titers were lower in patients with influenza than in respiratory syncytial virus-infected control subjects (P < .05), which suggests a protective effect of antibody. Interestingly, antibody titers did not differ between subjects with AD and those with NAD. Conclusion. In the absence of significant antigenic shifts, previous exposure to influenza, including vaccinations, may play a role in reducing the severity of influenza-associated lower respiratory tract disease.