Emergency Department Visits for Tick Bites

United States, January 2017-December 2019

Grace E. Marx, MD; Melanie Spillane, MPH; Alyssa Beck, MPH; Zachary Stein, MPH; Aaron Kite Powell, MPH; Alison F. Hinckley, PhD


Morbidity and Mortality Weekly Report. 2021;70(17):612-616. 

In This Article


Syndromic surveillance using NSSP data indicates high numbers and incidence of ED tick bite visits in the United States particularly during the late spring and early summer months, when nymphal blacklegged ticks are most active.[4] The number and rate of ED tick bite visits were highest in the Northeast, where Lyme disease is highly endemic and where tickborne disease risk might be well recognized.[5] Male patients, as well as very young (aged <10 years) and older patients (aged 50–79 years) were most likely to seek care at an ED for tick bites.

This analysis demonstrates that many patients are sufficiently concerned about tickborne diseases to seek care at an ED after a tick bite. However, ED visits likely represent only a fraction of the total health care impact of patients seeking care after a tick bite; a study in the United Kingdom showed that ED visits accounted only for approximately 12% of all health care visits by patients for arthropod bites, with most patients (67%) seeking care at outpatient clinics.[6] The bimodal seasonal distribution of ED tick bite visits is consistent with a New Hampshire study of ED encounters for Lyme disease.[7] In a prospective study, tick encounters were a strong predictor of tickborne diseases in the northeastern United States.[8] Findings from the current study closely parallel patterns seen in Lyme disease surveillance[5] that show that Lyme disease is reported more frequently among males and among very young and older persons, supporting the application of syndromic surveillance for tick bites as a harbinger for tickborne disease.

Syndromic surveillance represents the only national system currently available to track tick bites in humans and is a powerful complementary tool to traditional surveillance for tickborne diseases, particularly in areas with high incidence of Lyme disease, the most common U.S. tickborne disease. A major benefit of syndromic surveillance is its timeliness because most data are available within days of the health care visit. These data can guide actionable public health messaging. Tickborne disease prevention practices include avoiding tick habitats, wearing repellent consistently when outdoors, and performing regular tick checks during times of increased tick bite risk. After a high-risk tick bite, a timely single dose of doxycycline might be effective in preventing Lyme disease and is considered safe for all ages, including pediatric and geriatric populations.†† Another benefit of syndromic surveillance is its efficiency; because it relies on automated systems, it represents a lower cost in fiscal and human resources.

The findings in this report are subject to at least four limitations. First, the geographic granularity of these data is limited to HHS regions, which can comprise states and territories with heterogenous risks for tick exposure, ED data-sharing coverage with NSSP, and health care–seeking behavior. Given that most ED tick bite visits occurred in the Northeast, these trends might reflect primarily patient health care–seeking behavior in areas where Lyme disease is a major concern. County or state level data would reveal a more precise picture of tick bite risk and might be more informative for local public health action. Second, the query was limited to select combinations of words in patients' chief complaints and did not include any specific diagnostic or laboratory test codes. This might have led to misclassification that could have under- or overestimated the actual impact of ED tick bite visits. Medical record reviews of ED visits identified by the query could more thoroughly characterize this surveillance system by evaluating the sensitivity, specificity, and negative and positive predictive value of the syndromic surveillance query. Third, this analysis was limited to patients seeking care at an ED and does not represent all health care visits by patients seeking care after tick bites. The analysis was restricted to ED data because data available in NSSP are most complete for ED visits. Patients who are young, single, and employed might be more likely to visit an ED than an outpatient clinic[9] and might be overrepresented in this analysis. Finally, this analysis is based only on data from facilities that participate in NSSP and therefore is not generalizable to patients at nonparticipating facilities.

Syndromic surveillance for tick bites is valuable as a novel and efficient method to understand past trends and current risk for tick bites by region. By accessing these data through CDC's tick bite data tracker, a public-facing dashboard (https://www.cdc.gov/ticks/tickedvisits/index.html), public health practitioners and communities have access to immediately actionable data to guide public health messaging and individual tick bite prevention efforts (e.g., avoiding tick habitats, wearing repellent consistently when outdoors, and performing regular tick checks during times of increased tick bite risk). Educational campaigns that provide information to the public about how to safely remove ticks at home and when prophylactic antibiotics are indicated might be beneficial to reduce the impact on health care, associated health care costs, and personal risk for exposure to tickborne diseases.§§