Culture of all sputum samples irrespective of quality adds value to the diagnosis of pneumococcal community-acquired pneumonia in the elderly

Annika Saukkoriipi, Arto A Palmu, Jukka Jokinen, Annika Saukkoriipi, Arto A Palmu, Jukka Jokinen

Abstract

Culture of expectorated sputum in the microbiological diagnosis of community-acquired pneumonia (CAP) is considered valid only if high-quality (HQ) samples are obtained, but evidence regarding pneumococcal etiology specifically is lacking. We studied 323 radiologically confirmed CAP cases in patients aged ≥ 65 years. Sputum samples were assessed for quality microscopically and cultured. Two quality criteria sets were applied to delineate HQ from low-quality (LQ) sputa: leukocytes/epithelial cells ratio > 5 and ≤ 2.5 epithelial cells/400× magnification field (HQ1), or leukocytes/epithelial cells ratio > 1 (HQ2). A sputum sample was obtained and the quality assessed in 224 cases; 47% were HQ1 and 76% HQ2. Encapsulated pneumococci (EPnc) were cultured in 25 (24%), 14 (12%), 35 (21%), and 4 (7%) of the HQ1-, LQ1-, HQ2-, and LQ2-samples, respectively. If another pneumococcal test (blood culture, urine antigen, or ≥ twofold increase in CbpA or PsaA antibodies) was positive, EPnc were cultured at similar proportions in HQ1- and LQ1-sputa; if the other test was negative, EPnc were cultured less often in LQ1- than HQ1-sputa. EPnc were found less often in LQ2- than in HQ2-sputa. Our results suggest similar specificity in LQ- and HQ-sputum cultures. All sputum samples add value to the pneumococcal CAP-diagnosis in the elderly.

Keywords: Community-acquired pneumonia; Culture; Sputum; Streptococcus pneumoniae.

Conflict of interest statement

AS, AAP, and JJ are employees of the National Institute for Health and Welfare, which has received research funding from the GSK group of companies and Pfizer, Inc.

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Source: PubMed

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