Burden of Pertussis in Adults Aged 50 Years and Older: A Retrospective Database Study in England

Abstract

Introduction: Pertussis, a highly infectious respiratory disease caused by Bordetella pertussis, affects people of all ages. Older adults are particularly susceptible to its severe outcomes and complications.

Methods: In this retrospective cohort study, the incidence rate of pertussis among individuals aged ≥ 50 years was assessed during 2009-2018 using Clinical Practice Research Datalink and Hospital Episode Statistics databases, United Kingdom. Health care resource utilisation (HCRU) and direct medical costs (DMCs) were compared between patients with a pertussis diagnosis and propensity score-matched controls (matched on demographic and clinical variables).

Results: Among 5,222,860 individuals, 1638 had a pertussis diagnosis (incidence rate: 5.8 per 100,000 person-years; 95% confidence interval 5.5-6.0). Baseline (- 18 to - 6 months) HCRU and DMC were similar among 1480 pertussis patients and 1480 matched controls. However, there were increases in HCRU in the pertussis vs. matched cohort around the pertussis diagnosis (from months - 6 to - 1 to 5-11). The most notable increases (pertussis vs. controls) were in the rates of general practitioner (GP)/nurse visits (4.7-fold), clinical assessments (4.1-fold), and accident and emergency visits (3.0-fold) during the month before diagnosis and GP/nurse visits during the 2 months after diagnosis (2.5-fold) (all p < 0.001). DMCs were significantly higher in the pertussis cohort (p < 0.001). Total excess DMC in the pertussis cohort during months - 1 to + 11 was £318 per patient.

Conclusion: A pertussis diagnosis among adults aged ≥ 50 years resulted in significant increases in HCRU and DMC across several months around diagnosis. These results highlight the need for increased awareness of pertussis infection among adults aged ≥ 50 years and suggest that pertussis booster doses among this population should be considered.

Keywords: Direct medical costs; Health care resource utilisation; Incidence; Pertussis.

Fig. 1

Baseline (blue) and study periods (yellow). Square arrow ends indicate that the time period starts or ends exactly on the indicated time point; pointed arrow ends indicate that the time period ends the day before (for right-facing arrows) or starts the day after (for left-facing arrows) the indicated time point

Fig. 2

Incidence rate of reported pertussis among individuals aged ≥ 50 years: overall, by calendar year, and by age group. CI confidence interval, PYFU person-years of follow-up

Fig. 3

HCRU per 100 PY in the pertussis and controls cohorts. a GP/nurse and outpatient specialist visits; b GP prescriptions and clinical assessments; c A&E visits and hospitalisations^a. A&E accident and emergency, CI confidence interval, GP general practitioner, HCRU health care resource utilisation, PY person-years. ^aEvent rates and 95% CIs were estimated by fitting a negative binomial model. Uncorrected p < 0.001 (shown in bold) indicates statistically significant after cut-off adjustment for multiplicity. Uncorrected p < 0.05 is suggestive of a trend. p values were derived using the Wilcoxon rank-sum test

Fig. 4

Distributions of the proportions of patients with each number of GP/nurse visits in the pertussis and control cohorts during the month before index. GP general practitioner. ^aMann-Whitney U test for overall comparison between cohorts

Fig. 5

Monthly^a mean all-cause HCRU in the pertussis and control cohorts from – 18 months to 11 months around the index date (pertussis diagnosis). a GP/nurse visits; b GP prescriptions; c clinical assessments; d outpatient specialist visits; e A&E visits; f hospitalisations. A&E accident and emergency, GP general practitioner, HCRU health care resource utilisation. ^aMonths are labelled according to the start time of each interval, e.g., utilisation reported at 0 m is the average from day 0 to day 30

Fig. 6

Annualised DMC^a per individual in the pertussis and control cohorts during the various time periods of the study. p-values were calculated using the Wilcoxon rank-sum test. For details of the unit costs used, please see Supplementary Text S3. A&E accident and emergency, DMC direct medical costs, GP general practitioner, SD standard deviation. ^aValues above bars show total mean ± SD annualised DMC per individual. Absolute values can be found in Supplementary Table S9. ^bTop five prescription medications or clinical assessments (in the pertussis cohort; during each time period)