Most Lyme disease (LD) diagnoses among more than 88,000 US Medicare beneficiaries over a 4-year period occurred in the summer among men and those living in high-incidence states, and its overall incidence was about seven times higher than that reported through public health surveillance, finds a Centers for Disease Control and Prevention study published yesterday in Emerging Infectious Diseases.
The investigators compared rates of the tickborne illness from Medicare fee-for-service (FFS) data with those of surveillance data among adults aged 65 or older from 2016 to 2019.
Vast majority in high-incidence states
In total, 88,485 Medicare enrollees were diagnosed as having LD from 2016 to 2019, with an average incidence of 123.5 cases per 100,000 person-years, 7.4 times higher than the 34,183 cases picked up by surveillance during the same period (average rate, 16.6 cases/100,000 persons).
Roughly 82% of LD diagnoses occurred in high-incidence states. The median incidence was 346.9 per 100,000 person-years in high-incidence states, 35.3/100,000 person-years in states or jurisdictions bordering high-incidence states, and 29.4/100,000 person-years in low-incidence states.
Surveillance data, by contrast, showed that 93% of LD cases occurred among residents of high-incidence states. The median incidence was 57.1 per 100,000 people in high-incidence states, 3.6/100,000 persons in states abutting high-incidence states, and 0.6/100,000 persons in low-incidence states.
Most LD cases (57.8%) in Medicare enrollees were diagnosed from May through August, and 72.6% of cases reported in surveillance data occurred in the summer. The peak in surveillance cases was more prominent than that in Medicare-reported cases in all regions. A larger percentage of LD diagnoses occurred in winter in low-incidence areas.
Unique infection patterns in older adults
A total of 56.1% of LD cases were diagnosed in men per Medicare data, while 60.4% in men were represented in surveillance data. The median annual LD rate among male Medicare beneficiaries was 134.3 diagnoses per 100,000 person-years (range, 131.6 to 160.5 diagnoses/100,000 person-years).
The median annual LD rate among female beneficiaries was 109.5 diagnoses per 100,000 person-years (range, 103.3 to 125.7 diagnoses/100,000 person-years). In contrast, surveillance data showed a median annual incidence among men of 19.6 cases/100,000 people (range, 17.8 to 22.5), and a median annual incidence in women of 13.2 cases/100,000 people (range, 12.3 to 14.9).
We found that LD diagnoses identified from the Medicare FFS databases exhibit similar patterns to those of surveillance data, and that most diagnoses occur among residents of high-incidence states, in summer months, and among male beneficiaries.
Both Medicare and surveillance data revealed that men in high-incidence states had the highest LD rate for all age-groups. In adjoining states, Medicare data showed a slightly higher incidence among women than men in only the 65- to 69-year-old age-group, while surveillance data found that men had a higher incidence in all age-groups.
According to Medicare data, women in low-incidence states had a slightly higher LD incidence than men in only the 65- to 69-year-old age-group. In surveillance data, however, women had a higher rate than men among only those aged 75 to 79.
"We found that LD diagnoses identified from the Medicare FFS databases exhibit similar patterns to those of surveillance data, and that most diagnoses occur among residents of high-incidence states, in summer months, and among male beneficiaries," the authors concluded.
