Association between semi-quantitative microbial load and respiratory symptoms among Thai military recruits: A prospective cohort study 11 Medical and Health Sciences 1108 Medical Microbiology

Clarence C. Tam, Vittoria Offeddu, Katie B Anderson, Alden L. Weg, Louis R. Macareo, Damon W. Ellison, Ram Rangsin, Stefan Fernandez, Robert V. Gibbons, In Kyu Yoon, Sriluck Simasathien

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Background: Multiplex real-time polymerase chain reaction assays have improved diagnostic sensitivity for a wide range of pathogens. However, co-detection of multiple agents and bacterial colonization make it difficult to distinguish between asymptomatic infection or illness aetiology. We assessed whether semi-quantitative microbial load data can differentiate between symptomatic and asymptomatic states for common respiratory pathogens. Methods: We obtained throat and nasal swab samples from military trainees at two Thai Army barracks. Specimens were collected at the start and end of 10-week training periods (non-acute samples), and from individuals who developed upper respiratory tract infection during training (acute samples). We analysed the samples using a commercial multiplex respiratory panel comprising 33 bacterial, viral and fungal targets. We used random effects tobit models to compare cycle threshold (Ct) value distributions from non-acute and acute samples. Results: We analysed 341 non-acute and 145 acute swab samples from 274 participants. Haemophilus influenzae type B was the most commonly detected microbe (77.4% of non-acute and 64.8% of acute samples). In acute samples, nine specific microbe pairs were detected more frequently than expected by chance. Regression models indicated significantly lower microbial load in non-acute relative to acute samples for H. influenzae non-type B, Streptococcus pneumoniae and rhinovirus, although it was not possible to identify a Ct-value threshold indicating causal etiology for any of these organisms. Conclusions: Semi-quantitative measures of microbial concentration did not reliably differentiate between illness and asymptomatic colonization, suggesting that clinical symptoms may not always be directly related to microbial load for common respiratory infections.

Original languageEnglish (US)
Article number462
JournalBMC infectious diseases
Volume18
Issue number1
DOIs
StatePublished - Sep 14 2018

Bibliographical note

Funding Information:
This work was supported by the United States Department of Defense - Global Emerging Infectious Disease Surveillance (DoD - GEIS), Protocol 989A.

Publisher Copyright:
© 2018 The Author(s).

Keywords

  • Asymptomatic infection
  • Haemophilus influenza
  • Influenza
  • Influenza-like illness
  • Multiplex PCR diagnostics
  • Respiratory illness
  • Upper respiratory tract infection

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