Impact of microbial Aetiology on mortality in severe community-acquired pneumonia

Jessica Quah,Boran Jiang,Thean Yen Tan,Poh Choo Tan,Chuin Siau

doi:10.1186/s12879-018-3366-4

Abstract

BackgroundThe impact of different classes of microbial pathogens on mortality in severe community-acquired pneumonia is not well elucidated. Previous studies have shown significant variation in the incidence of viral, bacterial and mixed infections, with conflicting risk associations for mortality. We aimed to determine the risk association of microbial aetiologies with hospital mortality in severe CAP, utilising a diagnostic strategy incorporating molecular testing. Our primary hypothesis was that respiratory viruses were important causative pathogens in severe CAP and was associated with increased mortality when present with bacterial pathogens in mixed viral-bacterial co-infections.MethodsA retrospective cohort study from January 2014 to July 2015 was conducted in a tertiary hospital medical intensive care unit in eastern Singapore, which has a tropical climate. All patients diagnosed with severe community-acquired pneumonia were included.ResultsA total of 117 patients were in the study. Microbial pathogens were identified in 84 (71.8%) patients. Mixed viral-bacterial co-infections occurred in 18 (15.4%) of patients. Isolated viral infections were present in 32 patients (27.4%); isolated bacterial infections were detected in 34 patients (29.1%). Hospital mortality occurred in 16 (13.7%) patients. The most common bacteria isolated was Streptococcus pneumoniae and the most common virus isolated was Influenza A. Univariate and multivariate logistic regression showed that serum procalcitonin, APACHE II severity score and mixed viral-bacterial infection were associated with increased risk of hospital mortality. Mixed viral-bacterial co-infections were associated with an adjusted odds ratio of 13.99 (95% CI 1.30–151.05, p = 0.03) for hospital mortality.ConclusionsRespiratory viruses are common organisms isolated in severe community-acquired pneumonia. Mixed viral-bacterial infections may be associated with an increased risk of mortality.

Highlights

The impact of different classes of microbial pathogens on mortality in severe community-acquired pneumonia is not well elucidated
Our primary hypothesis was that respiratory viruses were important causative pathogens in severe community-acquired pneumonia (CAP) and was associated with increased mortality when present with bacterial pathogens in mixed viral-bacterial co-infections
One hundred seventeen patients were admitted to the medical intensive care unit for severe CAP within the study period

Summary

Introduction

The impact of different classes of microbial pathogens on mortality in severe community-acquired pneumonia is not well elucidated. Our primary hypothesis was that respiratory viruses were important causative pathogens in severe CAP and was associated with increased mortality when present with bacterial pathogens in mixed viral-bacterial co-infections. It was thought that viruses played a minor role in the pathogenesis of severe CAP, notwithstanding influenza epidemics [3]. Recent literature contradicts this and Advances in molecular techniques have improved the sensitivity, accuracy and turnaround time of microbial diagnostic tests [6, 7]. The reported incidence of viruses in severe CAP resulting in respiratory failure ranges 7.7% to 57% [4, 5]

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