The epidemiology of community acquired bacteremic pneumonia, due to Streptococcus pneumoniae, in the Top End of the Northern Territory, Australia—Over 22 years

Abstract

Background

Diseases caused by Streptococcus pneumoniae continue to cause substantial morbidity and mortality throughout the world. Furthermore, detrimental outcomes are more pronounced in some populations—such as those living in third world poverty, and Indigenous people who live in developed nations.

Methods

This study describes the epidemiology of blood culture positive S. pneumoniae community-acquired pneumonia (CAP) in the Top End of the Northern Territory of Australia. Demographics, indigenous status, medical risk factors, serotype and outcomes were collected from adults presenting to hospital with blood culture positive S. pneumoniae CAP, from 1987 to 2008.

Results

We report 205 cases, with a median age of 40 years. The average overall incidence rate ratio was 10.3 for indigenous adults compared with non-indigenous adults. There was no statistical difference between incidence rates pre and post-23-valent pneumococcal polysaccharide vaccine (23vPPV) introduction. Serotypes in presenting cases were predominantly (84.7%) 23vPPV types. The whole-population logistic regression model identified significant adjusted relative risks: 95% CI, for age 45 and older 1.6: 1.1, 2.2, indigenous 5.9: 3.7, 9.5, diabetes 2.3: 1.6, 3.3, excess alcohol 4.8: 2.8, 8.3, smoking 2.7: 1.9, 3.7 with indigenous + excess alcohol 18.5: 17.3, 19.7 as predictive for bacteremic S. pneumoniae CAP presentation.

Conclusions

Our results suggest that, the national 23vPPV program appears to be under-utilized. An integrated Public Health approach vigorously targeting indigenous adolescents, before substances such as alcohol and smoking are habitual, together with increased vaccine coverage, will reduce the burden of pneumococcal disease in this population.

Introduction

Streptococcus pneumoniae continues to be the leading causative agent for community-acquired pneumonia (CAP) in adults internationally [1], [2], [3]. Despite the breakthrough discovery of penicillin in 1928 and significant improvements in medical management of pneumonia, deaths continue to occur from S. pneumoniae CAP, especially for indigenous persons often at alarming rates [4], [5], [6], [7]. In Australia during the 1990s, respiratory disease was the leading cause of hospitalizations for Indigenous men, and the second highest for Indigenous women [8]. More recently, Indigenous adults continue to be hospitalized for respiratory diseases at four times the rate of non-Indigenous adults [9], with higher rates of non-vaccine serotype invasive pneumococcal disease (IPD) reported in Indigenous people [10], [11], [12], especially in the Northern Territory (NT). Furthermore, drug resistance to S. pneumoniae is worrisome, with the highest rate of intermediate penicillin susceptibility (34%) in Australia, reported from NT's capital city, Darwin [13].

The NT has the highest percentage of Indigenous residents (30%) in Australia, which compares with 2.5% nationwide [14]. Indigenous persons have higher rates of poor health and health risks, such as smoking; rates in remote-living Indigenous persons are higher still [15] Annual IPD rates in the NT are up to five times higher than the national average [12]. In 2009, the IPD rate for the NT was 40.5/100,000 population, compared with 7.2/100,000 population for Australia [12]. Furthermore, the ill health experienced by remote Indigenous residents overlies complex historical social struggles, creating even greater challenges for Public Health initiated disease prevention and reduction.

Vaccination appears to be a straightforward solution to reducing the burden of pneumococcal disease by; however, in practice it has proved an evasive target. The current national 23vPPV schedule includes: all Indigenous adults ≥15 years regardless of risk factors, with revaccination every 5 years to a maximum of three doses [16], [17]. For non-Indigenous Australians, the current recommendation is for persons aged ≥65 years, or ≥10 years with an underlying predisposing risk [17]. In the NT, serotypes contained in the 23-valent-pneumococcal polysaccharide vaccine (23vPPV) account for 85% of disease in non-Indigenous and 68% in Indigenous persons over 2 years of age [18]. However, there has been little evidence of a reduction of IPD in NT Indigenous adults [11], [16], [18], [19] since 23vPPV introduction in 1995. A recently published Cochrane review reports strong evidence for 23vPPV efficacy and effectiveness against bacteremic pneumococcal disease in adults [20]. Estimates of vaccine efficacy for invasive disease were 74% from randomized studies and 52% from observational studies; however, the meta-analysis failed to demonstrate vaccine efficacy in adults with chronic illness [20].

This study aims to establish the epidemiology of blood culture positive S. pneumoniae CAP over 22 years (1987–2008) of admissions to adult wards at Royal Darwin Hospital (RDH) the referring hospital for the NT. We aim to identify differences in presentation characteristics, serotypes and outcomes throughout the study period.