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.