Lack of discriminating signs and symptoms in clinical diagnosis of influenza of patients admitted to the hospital

Rapid diagnosis of influenza in hospitalised patients is important to prevent the transmission of the infection in the hospital. This prospective observational cohort study was designed to determine the relationship between the clinical diagnosis of influenza made by the physician at admission and the presence of influenza virus in patients with respiratory tract infections. This prospective observational cohort study was conducted in a large Dutch teaching hospital in a period of four weeks during the influenza season 2004/2005. All patients of 18 years and older, admitted with respiratory tract infections were included in the study. Clinical and laboratory parameters, chest radiograph (CR), blood and sputum cultures and nasopharyngeal swab for polymerase chain reaction (PCR) were obtained for each patient. In addition, the physicians opinion at admission whether this patient had influenza was recorded. A total of 78 patients were hospitalized with respiratory tract infections. In 41 (53%) of them influenza virus was detected by PCR. Among the patients that were positive for influenza virus by PCR, a clinical diagnosis of influenza was made in 18 cases (44%). Conversely, clinical diagnosis of influenza was made in 16 out of 37 patients in whom influenza virus was not detected by PCR. Neither C-reactive protein, leucocytes count nor an infiltrate on CR were helpful in determining the cause of the respiratory tract infection. The present findings failed to demonstrate a significant relationship between the clinical diagnosis of influenza and PCR detection of the virus. Also, the virus was present at least twice more often than influenza was clinically diagnosed. As a consequence, the decision to take protective measures to control spread of the virus should not rely on the clinical diagnosis.