Prospective comparative study of characteristics associated with influenza A and B in adults.

OBJECTIVES: To describe and compare the epidemiological characteristics associated with influenza type A and B as well as the characteristics associated with influenza pneumonia. The secondary objective was to evaluate the performance of influenza rapid diagnostic tests (RDT) in the emergency department.

PATIENTS AND METHODS: Prospective study, including 251 adult patients admitted to the emergency department during the 2013-2014 influenza outbreaks for flu-like illness confirmed by RT-PCR.

RESULTS: A total of 106 patients were infected with influenza type B (42%) and 145 with influenza type A (58%). Mean age was 56 and the sex-ratio was 0.9. In a multivariate analysis, the only factor independently related with the type of influenza strain was the patient's age. Overall, 17% of influenza-infected patients were vaccinated and 38% presented with pneumonia, with no significant difference between strains. In a univariate analysis, the risk factors associated with the occurrence of pneumonia were age, vaccination, and chronic obstructive pulmonary disease. Only 22% of samples positive by RT-PCR for influenza B and 40% for influenza A were positive by RDT.

CONCLUSION: Influenza type A and type B had similar clinical and biological signs, including severity. Influenza type B should not be neglected. Any emergency department may use the RDT for its ease-of-use and rapidity. However, its low sensitivity should be taken into consideration when interpreting results.