There is a high incidence of community-acquired pneumonia (CAP) in Kochi City in western Japan, which is primarily explained by the large proportion of elderly inhabitants, researchers report.
Konosuke Morimoto (Nagasaki University, Japan) and co-authors say that Streptococcus pneumoniae and respiratory viruses play an important role in CAP in the Kochi population. “Effective vaccination strategies […] must therefore be considered for elderly people,” they write in the Japanese Journal of Infectious Diseases.
Since little was known about the true burden and aetiological pattern of CAP in Japan, Morimoto’s team undertook a prospective, hospital-based surveillance study. They enrolled all patients with CAP who were aged 15 years or older and treated at a community-based private hospital in Kochi City, which the authors describe as “a typical rural city with a rapidly aging population”.
A total of 131 CAP patients were seen at the hospital over a 2-year period. Almost 70% of patients were male, the median age was 77 years and 60% of patients were 75 years or older.
The vast majority of patients needed in-hospital treatment and overall mortality was 4.6%. Around one-third had been prescribed antibiotics prior to their hospital visit.
Analysis of sputum and urine samples detected bacterial pathogens in 58.0% of CAP patients; S. pneumoniae and Haemophilus influenza were most common, being present in 28.2% and 18.3% of patients, respectively.
Additionally, 27.5% of samples were positive for at least one respiratory virus; human enterovirus or human rhinovirus were the most frequent, present in 13.3%.
“Intriguingly, patients infected with S. pneumoniae were more likely to have co-infection with respiratory viruses than other patients (50% vs 15%),” Morimoto et al remark.
The team also reviewed hospital data and identified an additional 185 CAP cases that were missed in their study; after including these, they estimate that the overall incidence rate of adult CAP in Kochi City was 9.6 per 1000 person–years.
The incidence rates increased with age, rising from 3.4 per 1000 person–years in those aged 15 to 64 years to 42.9 per 1000 person–years in those aged 75 years and older, a 12-fold increase.
The incidences of CAP associated with S. pneumoniae and respiratory viruses were also much higher in the older age group, at 10.01 and 11.13 per 1000 person–years, respectively.
Noting that this is the first study to investigate systematically age-stratified incidence of adult CAP in Japan, Morimoto et al conclude: “[O]ur study clearly demonstrated that the incidence of adult CAP among the Japanese population was high, probably reflecting the substantial aged population. The disease burden is likely to further increase as the population ages.”
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