Community-acquired pneumonia should not be regarded as a seasonal disease linked to winter, as it occurs throughout all four seasons, according to Spanish researchers.
However, they acknowledged that the pathogens that cause the condition are “clearly subject to seasonal variations”.
“This is the most comprehensive analysis of seasonal variations of aetiology”
The study, which was spread over more than a decade, involved 4,431 patients with community-acquired pneumonia at the Hospital Clinic of Barcelona.
Based on their findings, the researchers observed that community-acquired pneumonia occurred more frequently in winter than in other individual seasons.
However, they highlighted that, while 34% of cases happened during winter, two-thirds of cases occurred across spring, autumn and summer.
The researchers, led by a team from the University of Barcelona, also investigated the seasonal distribution of microbial aetiology in community-acquired pneumonia:
- Seasonal variations included Streptococcus pneumoniae – 21% in winter, versus 17% in spring, 14% in summer, and 13% in autumn
- Influenza viruses were most prevalent in autumn (6%) and winter (5%), compared with spring (3%) and summer (1%)
- Legionella pneumophila was most frequent in autumn (4%) and summer (4%), compared with spring (2%) and winter (1%)
- Incidence of polymicrobial pneumonia also differed between seasons – winter 7%, versus spring 5%, summer 3%, and autumn 6%
The study authors said: “Community-acquired pneumonia should not be regarded as a seasonal disease but occurs throughout all seasons.
“However, S. pneumoniae, influenza viruses, polymicrobial pneumonia and L. pneumophila are clearly subject to seasonal variations,” they noted in the journal Respirology.
“We observed a significant correlation between the lowest seasonal average temperature and polymicrobial pneumonia, pneumococcal pneumonia, and influenza viruses; conversely, L. pneumophila was more common when temperatures were higher,” they said.
They added: “To our knowledge, this is the most comprehensive analysis of seasonal variations of aetiology, based on prospectively collected data over 12 years of a large population with community-acquired pneumonia.”