Influenza virus infections are associated with high morbidity and mortality. Influenza activity varies worldwide, and regional detection is influenced by geographic conditions, demographic and patient-risk factors. We assessed influenza activity and patterns of seasonality during three consecutive years (2001-2003) in three risk groups in São Paulo city. Four-hundred-twelve outpatients with acute respiratory infection were subjected to epidemiological, clinical and laboratory investigations; these included community population (N=140), health-care workers (N=203), and renal-transplanted patients (N=69). Nasal wash samples were tested by direct fluorescent assay for influenza, parainfluenza, adenovirus, and respiratory syncytial virus. Overall Influenza positivity was 21%, and a progressive decline was observed in all groups over time. Influenza A and B co-circulated at the same time in 2001 and 2002, but not in 2003. Low influenza-vaccination rates (19%) were reported by health-care workers. Unexpected low levels of etiological agents were detected in renal-transplanted patients, and infected cases were less symptomatic than immunocompetent patients. Based on this study, we conclude that health-care worker-immunization programs should be implemented and the clinical patterns of infected influenza patients should be used as a guide for better case-definition criteria for adequate influenza surveillance, particularly for renal-transplant patients.
Influenza; risk groups; respiratory viral infection
