Staphylococcus aureus bacteraemia in a tropical setting: patient outcome and impact of antibiotic resistance

Abstract

Background: Most information on invasive Staphylococcus aureus infections comes from temperate countries. There are considerable knowledge gaps in epidemiology, treatment, drug resistance and outcome of invasive S. aureus infection in the tropics.

Methods: A prospective, observational study of S. aureus bacteraemia was conducted in a 1000-bed regional hospital in northeast Thailand over 1 year. Detailed clinical data were collected and final outcomes determined at 12 weeks, and correlated with antimicrobial susceptibility profiles of infecting isolates.

Principal findings: Ninety-eight patients with S. aureus bacteraemia were recruited. The range of clinical manifestations was similar to that reported from temperate countries. The prevalence of endocarditis was 14%. The disease burden was highest at both extremes of age, whilst mortality increased with age. The all-cause mortality rate was 52%, with a mortality attributable to S. aureus of 44%. Methicillin-resistant S. aureus (MRSA) was responsible for 28% of infections, all of which were healthcare-associated. Mortality rates for MRSA and methicillin-susceptible S. aureus (MSSA) were 67% (18/27) and 46% (33/71), respectively (p = 0.11). MRSA isolates were multidrug resistant. Only vancomycin or fusidic acid would be suitable as empirical treatment options for suspected MRSA infection.

Conclusions: S. aureus is a significant pathogen in northeast Thailand, with comparable clinical manifestations and a similar endocarditis prevalence but higher mortality than industrialised countries. S. aureus bacteraemia is frequently associated with exposure to healthcare settings with MRSA causing a considerable burden of disease. Further studies are required to define setting-specific strategies to reduce mortality from S. aureus bacteraemia, prevent MRSA transmission, and to define the burden of S. aureus disease and emergence of drug resistance throughout the developing world.

Figure 1. The burden of S. aureus bacteraemia is highest at the extremes of age, whilst mortality increased with age.

Age distribution and age-specific mortality rates and disease burden for 98 cases of S. aureus bacteraemia studied in Ubon Ratchathani, NE Thailand. Overall mortality increased significantly with age (p<0.001), analysing age as a continuous variable.

Figure 2. Survival from S. aureus bacteraemia is worse in adults than in children.

Kaplan-Meier survival curves comparing adult and paediatric patients with respect to S. aureus attributable deaths (p = 0.01). Non-attributable deaths were censored.

Figure 3. S. aureus attributable deaths occur more rapidly than non-attributable deaths.

Kaplan-Meier survival curves comparing S. aureus attributable deaths and non-attributable deaths (p = 0.001).