Low Prevalence of Pneumococcal Carriage and High Serotype and Genotype Diversity Among Adults Over 60 Years of Age Living in Portugal

PLoS One. 2014 Mar 6;9(3):e90974. doi: 10.1371/journal.pone.0090974. eCollection 2014.


Pneumococcal disease is frequent at the extremes of age. While several studies have looked at colonization among young children, much less is known among the elderly. We aimed to evaluate pneumococcal carriage among elderly adults living in Portugal. Between April 2010 and December 2012, nasopharyngeal and oropharyngeal swabs of adults over 60 years of age, living in an urban area (n = 1,945) or in a rural area (n = 1,416), were obtained. Pneumococci were isolated by culture-based standard procedures, identified by optochin susceptibility, bile solubility and PCR screening for lytA and cpsA, and characterized by antibiotype, serotype, and MLST. Associations between pneumococcal carriage, socio-demographic and clinical characteristics were evaluated by univariate analysis and multiple logistic regression. The global prevalence of carriage was 2.3% (95% CI: 1.8-2.8). In the multiple logistic regression analysis, smoking, being at a retirement home, and living in a rural area increased the odds of being a pneumococcal carrier by 4.4-fold (95% CI: 1.9-9.2), 2.0-fold (95% CI: 1.1-3.6) and 2.0-fold (95% CI: 1.2-3.5), respectively. Among the 77 pneumococcal isolates, 26 serotypes and 40 STs were identified. The most prevalent serotypes were (in decreasing order) 19A, 6C, 22F, 23A, 35F, 11A, and 23B, which accounted, in total, for 60.0% of the isolates. Most isolates (93.5%) had STs previously described in the MLST database. Resistance to macrolides, non-susceptibility to penicillin and multidrug resistance were found in 19.5%, 11.7%, and 15.6% of the isolates, respectively. We conclude that the prevalence of pneumococcal carriage in the elderly, in Portugal, as determined by culture-based methods, is low. Serotype and genotype diversity is high. Living in a rural area, in a retirement home, and being a smoker increased the risk of pneumococcal carriage. This study contributes to the establishment of a baseline that may be used to monitor how novel pneumococcal vaccines impact on colonization among the elderly.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Anti-Bacterial Agents / pharmacology
  • Carrier State
  • Drug Resistance, Bacterial
  • Female
  • Genes, Bacterial*
  • Genotype
  • Humans
  • Macrolides / pharmacology
  • Microbial Sensitivity Tests
  • Middle Aged
  • Multilocus Sequence Typing
  • Nasopharynx / microbiology
  • Oropharynx / microbiology
  • Penicillins / pharmacology
  • Pneumococcal Infections / epidemiology*
  • Pneumococcal Infections / microbiology
  • Portugal / epidemiology
  • Prevalence
  • Rural Population
  • Serotyping
  • Smoking
  • Streptococcus pneumoniae / drug effects
  • Streptococcus pneumoniae / genetics*
  • Streptococcus pneumoniae / growth & development
  • Streptococcus pneumoniae / isolation & purification
  • Urban Population


  • Anti-Bacterial Agents
  • Macrolides
  • Penicillins

Grant support

This work was partially supported by an unrestricted research grant from Pfizer (to RSL) and grant PEst-OE/EQB/LA0004/2011 (to the Oeiras Associated Laboratory) from Fundação para a Ciência e Tecnologia (FCT). SN was supported by grant SFRH/BD/40706/2007 from FCT, Portugal. The funders had no role in study design, data collection and analysis, preparation of the manuscript or decision to submit the manuscript for publication.