Pertussis prevention in older Australians with COPD or asthma needs a boost through increased community awareness and vaccination programs, according to new data.

A study, published in Emerging Infectious Diseases [link here], comprised an analysis of 992 patients ≥50 years of age with a clinical diagnosis of pertussis recorded in the IQVIA GP EMR database between 2015 and 2019.

The study found pertussis incidence rates decreased from 91.4 per 100,000 persons in 2015 to 57.6 per 100,000 in 2019.

Incidence rates (IRs) were consistently higher in women than men (110.5 v 74.5 per 100,000 persons) and highest in 50–64 year-olds compared to 65-74, 75-84 and ≥85 year-olds.

Patients with COPD or asthma had higher incidence rates of pertussis compared with the overall population ≥50 years of age.

On multivariate analysis, concurrent asthma conferred an adjusted overall risk (aOR) for pertussis of 2.94 and COPD 1.88.

A prior prescription of antibiotics for cough was also an important predictor of pertussis in older Australians (aOR 7.00) while a history of influenza vaccination reduce the risk of pertussis (aOR 0.38).

“Increased risk for pertussis in patients with COPD or asthma may be explained by potential adverse effects of inhaled or systemic corticosteroids, altered airway architecture, impairment of innate and acquired immunity, waning humoral immunity over time, and influence of concurrent conditions on immunogenicity,” the study said.

However the investigators said the lower risk for pertussis diagnosis in influence-vaccinated people may be artefact related to the lower risk for influenza-related worsening of other respiratory diseases and fewer potentially misdiagnosed pertussis cases.

They said uptake of pertussis immunisation at age 50 and 65 years is currently suboptimal yet “… timely pertussis vaccinations can protect vaccinated persons against pertussis development and prevent community-level transmission.”

“An effective vaccination strategy is necessary to reduce complications and increased healthcare costs associated with pertussis among patients with COPD or asthma,” they said.

“For patients with COPD or asthma who have unrecognised or undiagnosed pertussis, inappropriately prescribed antibiotics may empirically treat pathogens causing other respiratory illnesses but delay the diagnosis and control of pertussis.”

The study found laboratory tests for pertussis were ordered in only 24% of patients with a clinical diagnosis prompting a call for more testing in general practice enabling improved ascertainment of cases and timely treatment.