Cases of community-acquired pneumonia (CAP) are more frequent during the winter but can occur during other seasons, a new study says.
Researchers say the condition should not be considered a “seasonal disease,” and they noted that the number of infections with CAP pathogens such as Streptococcus pneumoniae, influenza viruses, Legionella pneumophila, or with more than one pathogen varies with the seasons.
Results of the study, “Seasonality Of Pathogens Causing Community-Acquired Pneumonia,” were published in the journal Respirology.
Researchers collected swabs from the back of the nose and throat, blood, serum, urine, sputum, and bronchoalveolar lavage (BAL) fluid from 4,431 CAP patients with a mean age of 66. CAP pathogens were identified in 1,756 people (40%).
They found that CAP cases most frequently occurred in winter (34%), but two-thirds of patients developed the condition during other seasons (less so in summer).
S. pneumoniae was the most common pathogen, found in 742 patients (17%), and 311 people (7%) had respiratory viruses. Ninety-seven patients (2%) had an L. pneumophila infection, and 242 (6%) had more than one pathogen (S. pneumonia and respiratory virus, followed by S. pneumonia and H. influenzae).
Pathogenic infections varied by season. S. pneumoniae infections were common in winter (21%), while influenza viruses were more common in autumn and winter (6% and 5%, respectively). L. pneumophila was frequently observed in the autumn and summer (4% each). Cases of patients having more than one pathogen (polymicrobial pneumonia) were more common in winter and spring (7% and 5%, respectively).
Researchers also found a connection between the lowest seasonal average temperature and cases of polymicrobial pneumonia, pneumococcal pneumonia, and influenza viruses. L. pneumophila infections occurred more often during warm weather, they found.
Mortality among patients was higher in winter compared to spring.
“(A)lthough there is considerable seasonal variability of pathogens in patients with CAP, especially for S. pneumoniae, influenza viruses, polymicrobial pneumonia and L. pneumophila, the disease should not be regarded as a seasonal disease but occurs throughout all seasons,” the researchers wrote. “Evidently, more investigation is required to understand the mechanisms behind seasonal variation patterns.”
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