Development of secondary bacterial pneumonia in adults presenting with influenza noninfluenza viral respiratory infection.

Background: Respiratory viral infections, particularly influenza, are known to cause significant morbidity and mortality, often due to secondary infections. Our aim was to comparatively analyze the incidence, epidemiology, and outcomes of secondary pneumonia in adult patients hospitalized with influenza noninfluenza viral infections and determine whether influenza particularly predisposes to secondary infections.

Methods: This was a retrospective analysis from a single tertiary medical center of adult patients admitted to the hospital between 2008 and 2010 with respiratory viral infections. Microbiological patterns and clinical outcomes were compared between those with influenza (VI,  = 57) and those with noninfluenza (NI,  = 77) respiratory viral infections.

Results: The NI group was older (60.6 ± 14.0 53.3 ± 19.7 years,  = 0.019) with higher rates of lung transplantation (29% 9%,  = 0.009) than VI. Overall, 35% developed secondary pneumonia, higher among NI (44%) than VI (23%,  = 0.017). was the most common cause of pneumonia in VI, whereas Gram-negative rods were most frequently identified in NI. The NI group had longer hospital [median 10 (interquartile range (IQR) 6-19) 6 (IQR 4-15) days,  = 0.019] and intensive care unit [median 4 (IQR 0-12) 0 (IQR 0-8) days,  = 0.029] stays compared with VI. Further, the NI group was more likely to be admitted to the intensive care unit compared with VI (62% 39%,  = 0.011). A trend towards increased mortality was observed in viral infections complicated by secondary pneumonia than primary viral infections (28% 15%,  = 0.122).

Conclusion: Secondary pneumonia is common among adults hospitalized with viral respiratory infections. Within our population, NI results in more frequent secondary pneumonia and longer hospital stays than those with VI. Given the high number of infections caused by Gram-negative rods, monitoring local epidemiology is critical for guiding initial antibiotic selection in empirical treatment of secondary infections.