Molecular surveillance on Streptococcus pneumoniae carriage in non-elderly adults; little evidence for pneumococcal circulation independent from the reservoir in children.

Anne L Wyllie,Krzysztof Trzciński,Astrid A T M Bosch,Jacob P Bruin,Alienke J Wijmenga-Monsuur,Lidewij W Rümke,Elisabeth A M Sanders,Nynke Y Rots,Kayleigh Arp

doi:10.1038/srep34888

Abstract

Carriage of Streptococcus pneumoniae in adults is rarely detected by the gold standard culture method. With molecular tests of high sensitivity now available, we analysed upper respiratory tract samples collected during autumn/winter 2012/2013 from parents of PCV7-vaccinated infants and from childless adults, directly comparing culture and qPCR-based S. pneumoniae detection. As compared to the gold standard of testing nasopharyngeal swabs, qPCR-based analysis of oral samples significantly improved detection of pneumococcal carriage (5% versus 20%, p < 0.0001) with higher carriage rates in parents compared to childless adults (34% versus 7%; p < 0.001). Molecular methods also increased the number of serotype-carriage events detected with higher carriage frequencies of serotypes 3 and 7A/F and lower of serotypes 6C/D and 15A/B/C in parents compared to their infant children. We provide evidence that culture-based methods severely underestimate adult carriage rates and for the superiority of testing oral samples over nasopharyngeal swabs. The substantial circulation of pneumococci in parents is however, not representative for the entire adult population. While age-associated differences in serotype carriage suggests reservoirs outside infants as potential sources of vaccine-serotypes contributing to weakening of vaccine herd effects, we find no evidence for reservoirs in adults contributing to serotype replacement in carriage.

Highlights

With molecular tests of high sensitivity available, we analysed upper respiratory tract samples collected during autumn/winter 2012/2013 from parents of PCV7-vaccinated infants and from childless adults, directly comparing culture and qPCR-based S. pneumoniae detection
Since we previously reported that (I) qPCR-based detection of S. pneumoniae in nasopharyngeal samples did not significantly increase the number of adult carriers detected compared to conventional culture alone and (II) it did not increase the overall number of adult carriers compared to molecular detection of S. pneumoniae in oropharyngeal samples[28,31], and (III) since we recently reported on the superiority of saliva over nasopharyngeal and oropharyngeal samples when tested in elderly with molecular methods[31], we decided not to investigate nasopharyngeal samples with molecular methods but to target oropharyngeal and saliva samples only
In line with our findings previously reported for parents[28], qPCR-based detection of S. pneumoniae in culture-enriched oropharyngeal samples alone was superior to culture-detection for nasopharyngeal and oropharyngeal swabs combined (n = 51, 8% versus n = 34, 5% of 621) albeit the difference did not reach statistical significance (Chi-Square, p = 0.07) (Table 2)

Summary

Introduction

With molecular tests of high sensitivity available, we analysed upper respiratory tract samples collected during autumn/winter 2012/2013 from parents of PCV7-vaccinated infants and from childless adults, directly comparing culture and qPCR-based S. pneumoniae detection. We recently reported on the superior sensitivity of molecular over culture methods[28,29] and of testing saliva instead of nasopharyngeal or oropharyngeal swabs for detecting carriers among school-aged children[30] and elderly[31].

Results

Conclusion