Tweak in surveillance leads to more reported Lyme disease cases in US
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Key takeaways:
- Lyme disease cases doubled in 2022 after the CDC changed the case definition for public health reporting.
- There were 62,551 Lyme disease cases reported to the CDC in 2022.
Although the number of reported Lyme disease cases in the United States in 2022 was nearly double the annual average from 2017 to 2019, the actual increase is not likely to have been that large, according to experts.
Writing in MMWR, Kiersten J. Kugeler, PhD, and colleagues from the CDC’s Division of Vector-Borne Diseases pinned the increase on a change to how Lyme disease is reported to the CDC’s National Notifiable Diseases Surveillance System (NNDSS).
According to the researchers, 62,551 Lyme disease cases were reported to the CDC in 2022 — 1.7 times the annual average of 37,118 from 2017 to 2019. Cases more than doubled among adults aged 65 years or older.
Prior to 2022, Lyme disease surveillance in the U.S. “required the collection of clinical information, most often coupled with laboratory evidence of infection, to classify cases,” Kugeler and colleagues explained.
In 2022, however, the Council of State and Territorial Epidemiologists and CDC revised the case definition for Lyme disease so that areas with a high incidence of infection could report cases “based on laboratory evidence alone, without the need to collect additional clinical information,” they wrote.
“Surveillance criteria — not clinical criteria — were changed to be less labor intensive and still give us an idea of what the trends are,” Paul G. Auwaerter, MD, MBA, clinical director in the division of infectious diseases and professor of medicine at the Johns Hopkins University School of Medicine, told Healio.
“So, you’re really trying to compare an apple from 2020 to a pear in 2022. Yes, they’re fruits, but they’re different,” said Auwaerter, who was not involved in the new study. “In 2 years, we can have a more meaningful conversation about what I think is happening.”
Based on data from the NNDSS for 2017 to 2019 and 2022, Kugeler and colleagues identified a 68% overall increase in Lyme disease, with the number of cases in high-incidence jurisdictions increasing by 72.9% and in low-incidence by 10%.
The researchers excluded cases reported in 2020 and 2021, the height of the COVID-19 pandemic, because of reporting anomalies.
Auwaerter said the benefit to the new surveillance method is that it will be helpful in states where Lyme disease is not yet endemic so that clinicians can be prepared.
“We’re looking for trends,” Auwaeter said. “Let’s say you’re in a county in North Carolina, where Lyme disease really hasn’t been accurately described, but suddenly you’re seeing increased numbers of Lyme tests that are consistent on a laboratory basis that are positive. That would be a signal that clinicians should be considering Lyme disease as a diagnosis and should be educated about Lyme disease.”
References:
- Kugeler KJ, et al. MMWR Morb Mortal Wkly Rep. 2024;doi:10.15585/mmwr.mm7306a1.
- CDC. NNDSS: Lyme disease (Borrelia burgdorferi) 2022 case definition. https://ndc.services.cdc.gov/case-definitions/lyme-disease-2022/. Last reviewed Aug. 30, 2021. Accessed Feb. 20, 2024.
Perspective
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There has been an increase in cases identified but not likely because there are a lot more cases occurring. It is just that people with a positive laboratory result are tabulated as a case without any clinical correlation. This is problematic because we know that the predictive value of a positive test is highly dependent on the pretest probably that a patient has Lyme disease — that is, the probability that the patient has Lyme disease before the Lyme titer is known based on the clinical and epidemiologic history (including likelihood of exposure to ticks) and the physical exam.
Unfortunately, many providers use Lyme titers as a screening test for patients with only nonspecific symptoms such as fatigue, pain and perceived cognitive difficulties. These symptoms are highly prevalent in the general population. The probability that a patient has Lyme disease if only nonspecific symptoms are present without any specific signs of Lyme disease (eg, facial palsy, arthritis), then some positive test results may be falsely positive.
On the other hand, most patients with early Lyme disease (ie, erythema migraines) — the most common manifestation of Lyme disease — typically will not have positive Lyme titers at the time they are seen, so many of these patients will be missed if not reported. I don’t think that we will know much about the accuracy of the large number of patients identified only by a positive laboratory test result until there is a review of the medical records of a large random sample of such patients.
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