Incidence and etiology of community-acquired pneumonia in the elderly in a prospective population-based study

Abstract

Background: We conducted a prospective population-based epidemiological study to prepare a setting for documentation of the efficacy of novel vaccines against pneumococcal (Pnc) community-acquired pneumonia (CAP) in the elderly. Specific objectives were to demonstrate setting feasibility, to construct a case definition for Pnc CAP, and to estimate its incidence. Methods: We prospectively enrolled patients with clinical and radiological findings compatible with CAP at municipal on-call clinics serving an elderly population (age ≥ 65 y) of approximately 29,500. Sputum, urine, nasopharyngeal swab (NPS), and blood samples were analyzed using diverse methods for the identification of Pnc (culture, PCR, antigen tests, serology) and of other pathogens. The following case definition for Pnc CAP was derived: encapsulated Pnc in blood culture or in high-quality sputum culture or at least 2 of the following: positive urine Pnc antigen; ≥ 2-fold increase in serum anti-PsaA or anti-CbpA antibodies; encapsulated Pnc culture or LytA PCR in either sputum or NPS. Results: We enrolled 490 clinical CAP patients during the 2-y follow-up, 53% of all clinical CAP patients in the source population; 323 were radiologically confirmed. The incidence of radiologically confirmed CAP was 5.5/1000 person-y (95% confidence interval (CI) 4.9–6.1) and 10.5/1000 person-y when adjusted for non-captured patients. The proportion of radiologically confirmed CAP caused by Pnc was estimated at 17%; i.e. 0.95/1000 person-y (95% CI 0.7–1.2) and 1.8 when adjusted for non-captured patients. Conclusions: We developed and documented a feasible methodology for capturing endpoints in a vaccine trial for the prevention of pneumonia. CAP incidence in the elderly population remains considerable and Streptococcus pneumoniae was one of the most commonly detected causative agents.

Keywords::

• Pneumonia
• Streptococcus pneumoniae
• incidence
• etiology
• population-based
• elderly

Acknowledgements

We are indebted to the Tampere city and Tampere University Hospital administration and personnel for their collaboration. We sincerely thank all the elderly participating subjects for consenting to the study during an acute illness. Other members of the Finnish Community-Acquired Pneumonia Study Group are the following: THL steering group members: Helena Käyhty, Pirjo H. Mäkelä, Maija Leinonen; study physicians: Sirkka-Liisa Kaistinen, Ritva Syrjänen, Stiina Zitting; study nurses: Päivi Siren, Mervi Mannila, Eija Lahtinen, Seija Nieminen, Nina Pere, Maiju Välimaa; bacteriology: Leena Erkkilä, Paula Asumaniemi, Katariina Autio, Aili Hökkä, Eeva-Liisa Korhonen, Leena Kuisma, Katja Nummilinna, Anu Ojala, Marika Vainio; virology: Titta Koivula, Esa Rönkkö; immunology: Merja Väkeväinen; data management: M. Grönholm, E. Koskenniemi, E. Ruokokoski; secretariat: Ulla Johansson, Merja Martenson; radiologists: reviewers Tiina Kauppinen and Tuula Vierikko, Finland and Charles White, USA. GSK Finland: Markku Pulkkinen; GSK Belgium: Jeanne-Marie Devaster, Isabelle Henckaerts, Thierry Pascal, Jan Poolman, Pierre Vandepapeliere. This study was conducted in collaboration with GlaxoSmithKline Vaccines, which supported the study process and participated in the design, interpretation, and writing of the manuscript.

Declaration of interest: The FinCAP Epi study was funded by GlaxoSmithKline. AAP has received travel expenses and honoraria from GlaxoSmithKline to attend expert group meetings and has had travel paid for by Merck to attend expert group meetings. He is the head of the Clinical Research Unit at the National Institute for Health and Welfare, which has received research funding from GlaxoSmithKline. JJ is the head of the Vaccine Research Unit at the National Institute for Health and Welfare, which has received research funding from GlaxoSmithKline. TM is director of the Department of Vaccination and Immune Protection at the National Institute for Health and Welfare, which has received research funding from GlaxoSmithKline. WPH and VV are shareholders and employees of GlaxoSmithKline. AS, MS, PT, TZ, TK: no conflicts of interest.