Scientists developed two models to figure out how many people get Lyme disease, also known as Lyme borreliosis (LB), each year. One model looked at blood samples from humans to find out how many people have been infected with the bacteria that causes Lyme disease. This model accounted for mistakes in test results using information from previous studies. The other model looked at infections in sentinel dogs to estimate how many people might get Lyme disease. They used data from Germany as a starting point for this model.

Both models used data from published studies to understand how often new cases happen (incidence), how many people have Lyme disease at any given time (prevalence), and the total number of people who have ever been infected (total infection burden). They used a more careful approach to estimate these numbers, looking at medical records and using a steady growth rate instead of assuming the number of cases grows quickly over time.

By averaging the two models, scientists came up with estimates for different countries and continents. For example, in 2018, the United States had about 473, 000 new cases each year, Germany had 471, 000, France had 434, 000, and the United Kingdom had 132, 000. Prevalence, or the number of people with Lyme disease at any time, was around 2. 4 million in the US, 2. 4 million in Germany, 2. 2 million in France, and 667, 000 in the UK. The total number of people who had ever been infected was estimated to be 10. 1 million in the US, 10. 0 million in Germany, 9. 3 million in France, and 2. 8 million in the UK.

Worldwide, the estimates for 2018 were 12. 3 million new cases each year, 62. 1 million people with Lyme disease at any time, and a total of 262. 0 million people who had ever been infected. These numbers are much higher than what health agencies have officially reported. They show that many cases are not diagnosed, and some are even misdiagnosed.

How Lyme Disease Spreads: A Look at Global Numbers

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