Researchers report that the incidence of Streptococcus pneumoniae infection has fallen significantly in the USA in the past decade but describe a “concerning trend” whereby the baseline health status of those with serious pneumococcal disease has worsened.
The team also reveals that the frequency of pneumococcus-associated invasive disease and mortality are significantly higher in unvaccinated as opposed to vaccinated patients.
“As the population ages and the chronic disease epidemic grows, the burden of pneumococcal disease is likely to increase thus highlighting the importance of pneumococcal vaccination”, write Kerry LaPlante (Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA) and co-authors in Infectious Diseases and Therapy.
The researchers used a national hospital database to identify all patients aged 50 years and over who tested positive for pneumococcal infection between 2002 and 2011. A total of 45,983 unique episodes were reported, of which 62.9% involved outpatients and 37.1% inpatients.
Over the study period, the incidence of pneumococcal disease decreased significantly in outpatients, from 5.8 to 2.9 infections per 100,000 clinic visits, but increased marginally in inpatients, from 262.3 to 328.1 infections per 100,000 hospital admissions. These changes equated to an annual decrease of 3.5% and an annual increase of 0.2%, respectively.
There were 14,511 episodes of serious S. pneumoniae infections. The most common was non-invasive pneumonia (63.4%), followed by bacteraemia (25.7%) and bacteraemic pneumonia (10.5%). Mortality in these patients was high, at 13.6% during hospital admission and 17.9% at 30 days.
Patients with serious S. pneumoniae infections had a high burden of comorbidities, with chronic respiratory disease and diabetes being the most common. The prevalence of six of eight major risk factors for S. pneumoniae infections rose significantly over the study period, the authors found.
Specifically, the prevalence of heart failure rose from 11.1% in 2002 to 18.6% in 2011, chronic respiratory disease from 33.1% to 50.9%, diabetes from 11.3% to 22.6%, liver disease from 4.6% to 7.4%, renal failure or dialysis from 5.6% to 13.8% and cancer from 13.0% to 18.9%. Only immunity disorder and HIV infection did not increase significantly.
Invasive disease and mortality prevalence were each significantly reduced in people who had received the pneumococcal vaccine in the 5 to 10 years preceding infection.
LaPlante and co-authors conclude: “Efforts to improve vaccination rates among high-risk patients may be an important strategy to mitigate increases in pneumococcal disease, however this requires further investigation.”
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