Association between semi-quantitative microbial load and respiratory symptoms among Thai military recruits: a prospective cohort study

• Published in: BMC infectious diseases Vol. 18; no. 1; p. 462
• Main Authors: Tam, Clarence C, Offeddu, Vittoria, Anderson, Kathryn B, Weg, Alden L, Macareo, Louis R, Ellison, Damon W, Rangsin, Ram, Fernandez, Stefan, Gibbons, Robert V, Yoon, In-Kyu, Simasathien, Sriluck
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 14.09.2018; BioMed Central; BMC
• Subjects: Analysis; Asymptomatic infection; Barracks; Cohort analysis; Colonization; Diagnosis; Diagnostic systems; Etiology; Health aspects; Illnesses; Infectious diseases; Influenza; Influenza-like illness; Microorganisms; Military; Military personnel; Multiplex PCR diagnostics; Multiplexing; Pathogens; Pharynx; Pneumonia; Polymerase chain reaction; Regression analysis; Regression models; Respiratory diseases; Respiratory illness; Respiratory syncytial virus; Respiratory tract; Respiratory tract diseases; Respiratory tract infections; Rhinovirus; Risk factors; Signs and symptoms; Streptococcus infections; Studies; Thais; Training; Upper respiratory tract infection; Thailand; Multiplex PCR diagnostics; Influenza-like illness; Upper respiratory tract infection; Influenza; Asymptomatic infection; Respiratory illness; Haemophilus influenza
• ISSN: 1471-2334; 1471-2334
• DOI: 10.1186/s12879-018-3358-4

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. 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. 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. 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.