Surveillance Case Definition Change Leads to 68.5% Increase in Reported Lyme Disease Cases in the US
In a surprising turn of events, the implementation of a revised surveillance case definition in 2022 has led to a staggering 68.5% increase in reported cases of Lyme disease in the United States. This significant rise in numbers has raised concerns among health officials and experts, prompting a closer look at the underlying factors contributing to this sudden surge.
The new data reveals that the increase in reported cases is particularly pronounced in high-incidence jurisdictions, where the number of cases has risen by 72.9%. On the other hand, low-incidence jurisdictions have seen a more modest increase of 10.0%. This disparity suggests that the change in surveillance methods has resulted in a greater number of cases being reported from areas with a higher risk of Lyme disease.
Before the implementation of the revised case definition, many cases from high-incidence jurisdictions would have been excluded due to the inability of health departments to obtain the necessary clinical information or inconsistencies with the specified criteria. However, with the new guidelines, these cases are now being included based on laboratory evidence alone. This change has shed light on the true extent of Lyme disease in these areas and highlights the importance of accurate reporting.
Interestingly, the increase in incidence is more pronounced among older age groups, with incidences more than doubling among adults aged 65 and above. There are several possible explanations for this trend. Firstly, older individuals may undergo more frequent laboratory testing, leading to a higher likelihood of detection. Secondly, disseminated illness, where the infection has spread throughout the body, may be more common among older age groups. Lastly, positive laboratory test results may be attributed to previous exposure to the bacteria rather than a current infection.
The timing of illness onset has also been affected by the change in surveillance methods. In high-incidence jurisdictions, where laboratory-based reporting is relied upon, the date of illness onset is rarely available. However, alternative dates related to laboratory testing or reporting still demonstrate a seasonal pattern, with a shift of two weeks later. This delay is attributed to the time required for the immune response to develop after symptom onset.
While the increase in reported cases is a cause for concern, it is important to acknowledge the limitations of the current surveillance system. Underreporting and overreporting are common issues, with early cases often being missed due to a lack of laboratory evidence. Previous case definitions relied on clinician reports, which were inconsistent among high-incidence jurisdictions. On the other hand, relying solely on serologic testing may result in the inclusion of nonincident cases or cases where another etiology is responsible for the illness.
Changes in laboratory testing methods may have also influenced the reported incidence of Lyme disease. The introduction of modified two-tier test (MTTT) serologic assays in 2019 has increased sensitivity in detecting early illness. However, challenges in implementing these assays within health departments have led to potential underascertainment of cases in 2022.
The implications for public health practice are significant. The increase in reported cases after the implementation of the revised surveillance case definition is likely a result of modified surveillance methods rather than a true change in disease risk. It is crucial for low-incidence jurisdictions to continue clinical investigations to accurately determine the probability of locally acquired infections and guide clinical and public education.
To improve standardization of surveillance data, specific codes have been created and approved for use in identifying persons with laboratory evidence of Lyme disease. The use of standardized codes by commercial and clinical laboratories is essential for consistent identification and reporting.
While the total number of reported cases has increased, it still falls short of the estimated 476,000 Lyme disease diagnoses that occur annually in the United States. This alarming frequency highlights the urgent need for effective prevention methods to combat this persistent and potentially debilitating disease.
In conclusion, the change in surveillance case definition has led to a significant increase in reported cases of Lyme disease in the United States. The rise in numbers is primarily seen in high-incidence jurisdictions, with older age groups being disproportionately affected. While the revised approach to surveillance improves standardization, it also poses challenges in comparing trends with previous data. The need for accurate reporting and effective prevention methods remains paramount in addressing the growing threat of Lyme disease.
