Identification and prevalence of bacteria causing atypical pneumonia in patients with severe respiratory illness and influenza-like illness in South Africa, 2012-2013
Date
2016-02-15
Authors
Carrim, Maimuna
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Atypical pneumonia-causing bacteria contribute considerably to community-acquired pneumonia (CAP), however this contribution is largely underestimated due to the difficulty in identifying these organisms and limited studies targeting them. Rapid diagnostic tools such as real-time polymerase chain reaction (PCR) help to overcome the difficulty in identifying atypical pneumonia-causing bacteria. Our aim was to establish a real-time PCR assay for identification of atypical pneumonia-causing bacteria and determine the prevalence of atypical pneumonia-causing bacteria (Mycoplasma pneumoniae, Legionella spp. and Chlamydia (Chlamydophila) pneumoniae) in South Africa.
We enrolled severe respiratory illness (SRI) patients, influenza-like illness (ILI) patients and controls prospectively from June 2012 through December 2013 at two hospitals and two out-patient clinics located in two provinces of South Africa. Demographic, clinical and in-hospital outcome data were collected. Naso-oropharyngeal specimens were collected from all patients and induced sputa were collected from SRI patients only. Total nucleic acids were extracted from clinical specimens and were tested for M. pneumoniae, C. pneumoniae, Legionella spp. and human RNAseP by a multiplex real-time PCR assay. Macrolide susceptibility testing using high-resolution melt-curve analysis (HRM) and multiple-locus variable-number tandem-repeat analysis (MLVA) was performed on 94% (75/80) of M. pneumoniae-positive specimens. M. pneumoniae-positive specimens were cultured and P1 typing was performed on culture-positive specimens using HRM. We described trends in disease by age-group, time, gender, HIV prevalence, symptom duration, underlying conditions and clinical outcome. For the comparative analysis the χ2 test and univariate
logistic regression was performed. Statistical significance was assessed at P<0.05 for all parameters.
From June 2012 through December 2013, 6122 patients were enrolled. Real-time PCR for the identification of the atypical pneumonia-causing bacteria was performed on 85% (5210/6122) of cases which included 86% (2793/3239) of SRI patients, 86% (1670/1940) of ILI patients and 79% (747/943) of controls. The percentage of patients tested by age group was 15% (783/5183), 15% (779/5183), 10% (536/5183), 9% (466/5183), 31% (1603/5183), 16% (827/5183), 4% (189/5183) amongst those aged <1 years, 1-4 years, 5-14 years, 15-24 years, 25-44 years, 45-64 years and ≥65 years, respectively. A total of 4534 of 5210 patients (87%) had a known HIV status of which 2148/4534 (47%) were HIV infected.
The prevalence of atypical pneumonia-causing bacteria among SRI patients in two hospitals in South Africa was 3.3% (91/2793), with a prevalence of 1.5% (25/1670) and 1.3% (10/747) amongst patients with ILI and asymptomatic controls, respectively.
The prevalence of M. pneumoniae was 2.1% (59/2793) among SRI patients, 1% (16/1670) among ILI patients and 0.4% (3/747) among controls. M. pneumoniae detection was significantly higher amongst individuals aged <5 years (2.6%; 41/1563) compared to individuals ≥5 years (1%; 37/3624) (P<0.001). M. pneumoniae cases were detected throughout the study period. The overall attributable fraction of M. pneumoniae for patients with SRI, was 89.0% (95% confidence interval [CI] 48.7 – 97.5), after adjusting for age and HIV status. A culture was obtained for 11/75 (15%) of the M. pneumoniae-positive specimens. The isolates were distributed into 4/11 (36%), 4/11 (36%) and 3/11 (27%) for P1 type 1, type 2 and a variant of type 2, respectively. Analysis of the combination of tandem
repeats at the four MLVA loci, revealed three distinct MLVA types namely 3562 (43%; 16/37), 3662 (41%; 15/37) and 4572 (16%; 6/37). In M. pneumoniae-positive specimens with susceptibility profiles available (43%; 32/75), the mutation conferring macrolide resistance was absent in all (100%; 32/32) cases.
When comparing specimen types for the detection of Legionella spp. a significant difference was observed [16/16 (100%) induced sputum-positive vs. 0/16 (0%) nasopharyngeal specimens-positive; P<0.001] between the specimen types. Legionella spp. were only detected in SRI patients, with a prevalence of 0.8% (21/2793). Furthermore, among SRI patients, the organism was only detected in patients 15 to 64 years old [2% (3/155) in 15-24 year, 1.1% (10/939) in 25-44 year and 1.5% (8/530) in 45-64 year age groups]. There was no difference in prevalence of Legionella spp. between the two SRI sites [6/1312 (0.5% at Edendale hospital vs. 15/1481 (1%) at Klerksdorp-Tshepong hospital; P=0.14]. Legionella spp.-positive patients were more likely to have chronic symptom duration >7 days [15/19 (79%) Legionella positive vs. 1125/2728 (41%) Legionella negative, P=0.003]. A species was only identified for 1 of the 21 cases, and the species was identified as L. pneumophila serogroup 1.
The prevalence of C. pneumoniae was 0.4% (11/2793) among patients with SRI, 0.5% (9/1670) among patients with ILI and 1% (7/747) among asymptomatic controls. There was no statistically significant difference identified in the detection rate of C. pneumoniae between patients with SRI or ILI and controls as the attributable fraction was calculated to be -31% (95% CI –276.75 – 54.28) for SRI cases and -111% (95% CI -629.2 – 38.7) for ILI cases compared to controls.
Our study presented the utility of a multiplex real-time PCR assay for the identification of atypical pneumonia-causing bacteria. This study helps bridge the gap of limited data in South Africa and provides baseline data that can be used for future surveillance programs in the hope of better understanding atypical pneumonia-causing bacteria.
Description
Dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg in fulfillment of the requirements for the degree of Master of Science in Medicine.
Johannesburg, 2015