High healthcare resource utilisation due to pertussis in Australian adults aged 65 years and over
Introduction
Pertussis, more commonly known as whooping cough, is a highly contagious acute upper respiratory tract infection caused by the Bordetella pertussis bacterium. In recent years, there has been increased recognition of pertussis disease amongst adults, especially in those aged over 50 years old [1], [2], [3], [4]. While most pertussis infection among older adults is sub-clinical, symptomatic disease also frequently occurs and can result in substantial economic burden [4], [5], [6]. Pertussis symptoms generally persist for 3–4 months but can last for up to 6 months after infection [7] with the potential for a corresponding increase in healthcare utilisation over this period.
While most symptomatic cases only present with symptoms such as prolonged coughing, more severe complications do occur in adults. There is evidence that the median length of pertussis-associated hospital stay among the elderly (around 7–9 days) is twice as long as the median for infants under 6 months of age [8] and fatalities from pertussis infection in adults aged 60 years have been reported [9]. Pertussis-associated healthcare burden may also be further exacerbated by co-morbidities which increase with age. For instance, there is evidence of increased healthcare utilisation among cases with either chronic obstructive pulmonary disease (COPD) or asthma [10].
The increased recognition of pertussis [3] among older adults highlights the need to better understand healthcare utilisation in these patients. However, there are few comprehensive studies on healthcare use in this population, especially in Australia where to our knowledge, there has been no large-scale population-based study on this topic. Previous published studies have either been limited in both sample size and geographical scope [5], [11] or have examined cases alone without comparison with matched controls [12], [13]. The 45 and Up Study cohort [14] provides an opportunity to derive robust estimates of pertussis-attributable healthcare utilisation.
In this study, we adapted a case-control design used previously in the context of herpes zoster [15] with the aim to produce detailed and internally validated estimates of pertussis-related healthcare utilisation in older adults in the 45 and Up Study cohort. As there are proposed vaccination strategies around older adults (65+ years) or with existing co-morbidities, we also aimed to quantify the effects of age, self-reported asthma and body mass index (BMI) status on healthcare utilisation.
Section snippets
Study setting, design, and participants
To estimate excess healthcare resource utilisation among adults notified for pertussis we used the Sax Institute’s 45 and Up Study cohort. Briefly, the cohort comprises of 267,153 adults 45 years of age residing in the state of New South Wales (NSW), Australia (about 10% of all adults in the age range living in NSW, Australia’s most populous state) recruited between January 2006 up to December 2009 [14]. Prospective participants were randomly sampled from the Department of Human Services
Descriptive statistics
There were 1222 notified pertussis cases in the cohort, of which 524 were PCR-confirmed, leading to 524 case-control pairs in our main analysis. Of these pairs, 64% were females, 85% were notified during the most recent epidemic period (2008–12) and 59% notified during the spring and summer seasons. The median age at first incident pertussis notification was 64 years. Table 1 summarises other characteristics of the matched case-control pairs. Results from Kolmogorov-Smirnov tests showed no
Discussion
We found significant increases in outpatient healthcare burden among pertussis cases with an average excess of 2.5 prescriptions dispensed (1.1 antibiotic prescriptions), 0.1 ED admissions, and 2.3 GP presentations for every PCR-confirmed pertussis notification in adults aged 45 years. Age-group comparisons showed substantially higher excess healthcare utilisation for those aged ≥65 years compared to those aged 45–64 years with a significant increase in excess all prescriptions dispensed (1.1
Limitations
The 45 and Up Study cohort has known biases such as over-sampling of rural populations and people aged 80+, a healthier population than average on some dimensions (e.g., better access to healthcare facilities and lower proportion of smokers) and a participation rate of ~18% [14], all of which mean that caution should be exercised in generalising our results to the general population. In addition, risk factors such as asthma and BMI status were identified at baseline survey and may not have
Conclusion
We found substantial excess in outpatient healthcare burden among adults aged 65 years and over notified with pertussis. The high burden of healthcare use in this age group supports further evaluation of prevention of pertussis in this population.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was completed using data collected through the 45 and Up Study (www.saxinstitute.org.au). The 45 and Up Study is managed by the Sax Institute in collaboration with major partner Cancer Council NSW; and partners: The National Heart Foundation of Australia (NSW Division); NSW Ministry of Health; NSW Government Family & Community Services – Ageing, Carers and the Disability Council NSW; and the Australian Red Cross Blood Service. We thank the many thousands of people participating in
Financial support
RN Leong is supported by the University International Postgraduate Award (UIPA) for study toward a PhD in the Faculty of Medicine, School of Public Health and Community Medicine, University of New South Wales, Australia. B Liu is supported by an Australian National Health and Medical Research Council (NHMRC) fellowship. Access and use of the 45 and Up Study was funded by the Australian National Health and Medical Research Council Grant #1107008.
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