How a new surveillance method is identifying more cases of Lyme disease in the US

Diseases spread by ticks and other insects are becoming more common in the United States, but a new methodology for tracking Lyme disease may overestimate the significant spike in cases seen in 2022.

There were more than 62,000 cases of Lyme disease reported to the US Centers for Disease Control and Prevention in 2022 – nearly a 70% jump from the annual average from 2017 to 2019, according to a report published by the agency on Thursday.

But this sharp increase “likely reflects changes in surveillance methods rather than change in disease risk,” according to the CDC.

The vast majority of Lyme disease cases in the US are reported from just over a dozen jurisdictions in the Northeast, mid-Atlantic and upper-Midwest where ticks are particularly prevalent. In 2022, the Council of State and Territorial Epidemiologists revised the criteria for reporting a Lyme disease case, allowing these high-incidence jurisdictions to report cases based solely on laboratory evidence without the need to confirm with the collection of additional clinical information from patients.

Before 2022, some cases may not have been reported because health departments couldn’t confirm the clinical information, according to the CDC report. This shift may help ease the workload for public health workers, as rising infection rates had already created challenges in some jurisdictions. The new methods may also help capture more cases and offer better overall insights and comparison of trends across jurisdictions, but they will create challenges for tracking against historical trends from before the change.

Despite the significant spike, the number Lyme disease cases that are reported to the CDC is just a fraction of the estimated number of total cases. There are about 476,000 estimated diagnoses of Lyme disease in the US each year – nearly eight times more than even the improved surveillance methods captured in 2022.

Vector-borne diseases – spread by biting insects and arachnids such as ticks, mosquitoes, fleas and lice – are a significant and rising public health threat. Cases have doubled in the US over the past two decades, according to the CDC.

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Lyme disease is the most common vector-borne disease in the US, along with Zika virus, West Nile virus, dengue, malaria, plague, Rocky Mountain spotted fever and alpha-gal syndrome.

Earlier this month, the US Department of Health and Human Services launched a national public health strategy to prevent and control vector-borne diseases in people. The plan brings together 17 federal departments and agencies to better understand the spread of diseases and develop tools to diagnose and treat them.

“Due to shifting land use patterns, global travel and trade, and a changing climate, the threat of existing and emerging vector-borne diseases continues to grow,” HHS wrote in a news release about the new strategy. “As geographic ranges of vectors expand, the number of pathogens spread by vectors continues to climb—yet only one vaccine is available to protect people against almost 20 domestic threats.”