Clinical and economic burden of pneumococcal disease in older US adults
Introduction
Streptococcus pneumoniae (pneumococcus) causes significant morbidity and mortality worldwide in both children and adults. The most important pneumococcal infections are invasive pneumococcal disease (IPD) – including meningitis, bacteremia/septicemia, and bacteremic pneumonia – and nonbacteremic pneumococcal pneumonia (NPP), because of their high case-fatality rates and economic costs, and in the case of NPP, its relatively high incidence rate. The introduction and widespread use of the 7-valent pneumococcal conjugate vaccine (PCV7) among young children beginning in year 2000 has greatly reduced the burden of IPD and pneumococcal pneumonia in this age group, and has indirectly resulted – via a herd effect – in reduced levels of IPD among older adults (i.e., persons aged ≥50 years) [1], [2], [3]. However, despite the indirect benefit from childhood vaccination and the availability of a 23-valent polysaccharide pneumococcal vaccine (PPV23) – currently recommended for persons aged 65 years and older as well as younger persons with certain underlying medical conditions – the burden of pneumococcal disease in older adults remains substantial.
Estimation of the clinical burden of IPD is a relatively straightforward exercise because of the highly specific definition of this disease – isolation of pneumococcus from a normally sterile site, such as blood or cerebrospinal fluid. Estimation of the burden of NPP is more problematic, for several reasons. First, the diagnosis of pneumonia can be confused with several other common infectious and non-infectious diseases, including bronchitis, congestive heart failure, pulmonary infarction, and atelectasis. Second, the causative pathogen is not identified for the great majority of pneumonia cases, and thus the percentage of all pneumonia cases that is due to pneumococcal infection is uncertain.
A thorough analysis of the overall burden of pneumococcal disease among US older adults, including the total number of cases, case-fatalities, direct healthcare costs, and the value of morbidity- and mortality-related work loss, has not been reported. Knowledge of this burden, combined with the increasing prevalence of antibiotic-resistant strains of S. pneumoniae, may motivate greater efforts to prevent and control these diseases. Moreover, because conjugate pneumococcal vaccines are currently in development for use in all adults aged 50 years and older, data on the burden of pneumococcal disease among persons in this age group will be important for making informed decisions regarding the allocation of healthcare resources and evaluating the public health and economic impact of alternative strategies for preventing pneumococcal disease, including age- and/or risk-based vaccination programs. We therefore undertook a detailed analysis of the annual burden of pneumococcal disease among US adults aged 50 years and older, on an overall basis as well as stratified by age and risk profile.
Section snippets
Model overview
We estimated the expected current annual clinical and economic burden of pneumococcal disease among US adults aged 50 years and older by combining age- and risk-group data on rates and costs of disease and case-fatality rates, with the corresponding estimates of population size. Pneumococcal disease included IPD (bacteremia/septicemia [hereafter, “bacteremia”] and meningitis) and NPP (stratified based on setting of care – inpatient care versus outpatient care only); all cases of IPD were
Basecase analyses
Among the 91.5 million US adults aged ≥50 years, 29,500 cases of IPD (including 27,700 cases of bacteremia and 1,800 cases of meningitis), 502,600 cases of NPP (including 198,600 cases requiring inpatient care and 304,000 requiring outpatient care only), and 25,400 pneumococcal-related deaths (including 6200 due to IPD and 19,200 due to NPP) are estimated to occur on an overall basis yearly (Fig. 1, Table 2). Annual direct and indirect costs due to pneumococcal disease in this age group are
Discussion
Using a model combining age- and risk-group-specific data on rates and costs of disease (and associated case-fatality rates) with corresponding estimates of population size, we found that the annual clinical and economic burden of pneumococcal disease among US adults aged 50 years and older is substantial – 29,500 cases of IPD, 502,600 cases of NPP, $3.7 billion in total direct costs, and $1.8 billion in total indirect costs. To the best of our knowledge, our study is the first to assemble
Acknowledgments
Funding for this study was provided by Wyeth Research to Policy Analysis Inc. (PAI). Derek Weycker, Ph.D. and John Edelsberg, M.D., M.P.H. are employed by PAI. David Strutton, Ph.D., M.P.H. and Reiko Sato, Ph.D. are employed by Wyeth Research. Lisa Jackson, M.D., M.P.H. is employed by the Group Health Center for Health Studies.
References (38)
- et al.
Decline in pneumonia admissions after routine childhood immunisation with pneumococcal conjugate vaccine in the USA: a time-series analysis
Lancet
(2007) - et al.
Impact of the introduction of pneumococcal conjugate vaccine on rates of community acquired pneumonia in children and adults
Vaccine
(2008) - et al.
Prospective multicenter study of the causative organisms of community-acquired pneumonia in adults in Japan
J Infect Chemother
(2006) - et al.
Microbiological profile of community-acquired pneumonia in adults over the last 20 years
J Infect
(2005) - et al.
Is Streptococcus pneumonia the leading cause of pneumonia of unknown etiology? A microbiologic study of lung aspirates in consecutive patients with community-acquired pneumonia
Am J Med
(1999) - et al.
Microbiological etiology in clinically diagnosed community-acquired pneumonia in primary care in Orebro, Sweden
Clin Microbiol Infect
(2003) - et al.
Alternative strategies for adult pneumococcal polysaccharide vaccination: a cost-effective analysis
Vaccine
(2008) - et al.
Treatment cost of community-acquired pneumonia in an employed population
Chest
(2004) - et al.
The influence of the severity of community-acquired pneumonia on the usefulness of blood cultures
Respir Med
(2001) - et al.
Randomised trial of 23-valent pneumococcal capsular polysaccharide vaccine in prevention of pneumonia in middle-aged and elderly people
Lancet
(1998)