Emergency Department Visits for Tick Bites — United States, January 2017–December 2019

Grace E. Marx, MD1; Melanie Spillane, MPH1; Alyssa Beck, MPH1; Zachary Stein, MPH2; Aaron Kite Powell, MPH2; Alison F. Hinckley, PhD1 (View author affiliations)

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Summary

What is already known about this topic?

Tickborne diseases are spread by the bites of infected ticks; approximately 50,000 cases of tickborne diseases are reported in the United States each year. National surveillance for tick bites is not currently available.

What is added by this report?

A novel query of National Syndromic Surveillance Program data indicated that one out of every 2,000 emergency department visits are for tick bites, with higher incidence during the spring and early summer and in the Northeast.

What are the implications for public health practice?

Syndromic surveillance data for tick bites can guide timely, actionable public health messaging such as avoiding tick habitats, wearing repellent consistently when outdoors, and performing regular tick checks during times of increased tick bite risk.

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The incidence of tickborne diseases in the United States is increasing; reported cases more than doubled from >22,000 in 2004 to >48,000 in 2016 (1). Ticks are responsible for approximately 95% of all locally acquired vectorborne diseases reported by states and the District of Columbia, with Lyme disease accounting for >80% of those cases (2). After a tick bite, persons might seek care at an emergency department (ED) for tick removal and to receive postexposure prophylaxis, which has been shown to effectively prevent Lyme disease when taken within 72 hours of a high-risk bite (3). Using data from CDC’s National Syndromic Surveillance Program (NSSP), investigators examined ED tick bite visits during January 2017–December 2019 by sex, age group, U.S. region, and seasonality. During this 36-month period, 149,364 ED tick bite visits were identified. Mean cumulative incidence was 49 ED tick bite visits per 100,000 ED visits overall; incidence was highest in the Northeast (110 per 100,000 ED visits). The seasonal distribution of ED tick bite visits was bimodal: the larger peak occurred during the spring and early summer, and the smaller peak occurred in the fall. This pattern aligns with the seasonality of a known and abundant human-biter, the blacklegged tick, Ixodes scapularis (4). Compared with other age groups, pediatric patients aged 0–9 years accounted for the highest number and incidence of ED tick bite visits; incidence was higher among male patients than among females. Tick bites are not monitored by current surveillance systems because a tick bite is an event that in and of itself is not a reportable condition to health departments. Syndromic surveillance of ED tick bite visits can provide timely information that might predict temporal and geographic risk for exposure to tickborne diseases and guide actionable public health messaging such as avoiding tick habitats, wearing repellent consistently when outdoors, and performing regular tick checks during times of increased tick bite risk.

Health care visits were identified using CDC’s NSSP BioSense Platform, which hosts a national public health surveillance system that aggregates data by U.S. Department of Health and Human Services (HHS) geographic regions.* By the end of calendar year 2019, NSSP included data from an estimated 71% of all ED visits in the United States, with 3,206 ED facilities actively contributing data. Health care visits at facilities categorized as EDs were included in this analysis; other visit categories such as inpatient hospitalizations, urgent care, or outpatient clinic visits were excluded. Data were extracted using the Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE),§ a tool in the BioSense Platform. In collaboration with syndromic surveillance and vectorborne disease epidemiologists from states with high incidences of tickborne diseases, a query was developed to identify ED visits by patients with a chief complaint for ticks or tick bites. The query used Boolean operators (e.g., tick or tick and bite) and included common misspellings. Diagnostic codes specific to tick bites were not available in any of the diagnostic code classification systems, including the ninth and tenth revisions of the International Classification of Diseases and so were not included in the query.

The tick bite query was applied to all ED visits during January 1, 2017–December 31, 2019, available in ESSENCE to identify ED tick bite visits. Absolute counts and incidence of ED tick bite visits were computed by sex, age group, month, and geographic region. Incidence was calculated by dividing the number of ED tick bite visits by the total number of ED visits in ESSENCE in that category, multiplied by 100,000. These data were also used to create a public-facing, interactive visualization tool** to allow the public to explore the data for ED tick bite visits by region, month, and basic patient demographic characteristics.

During 2017–2019, the mean annual number of ED tick bite visits was 49,788 (mean incidence = 49 per 100,000 ED visits) (Table); the mean annual number (31,340) and incidence (110 per 100,000 ED visits) were highest in the Northeast region. Males accounted for the majority (57%) of ED tick bite visits. The mean number (10,142) and incidence (86 per 100,000 ED visits) of ED visits for tick bites were highest among pediatric patients aged 0–9 years; a second peak occurred among patients aged 70–79 years (64 per 100,000 ED visits). Seasonality was bimodal, with the first and larger peak during April through July and a second smaller peak in October through November (Figure).

Discussion

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.§§

Acknowledgments

Lyme Disease High Incidence States Collaborative; members of the National Syndromic Surveillance Program Community of Practice Syndrome Definition Committee; state and local health departments participating in CDC’s National Syndromic Surveillance Program.

Corresponding author: Grace E. Marx, gmarx@cdc.gov, 970-266-3583.


1Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC; 2Center for Surveillance, Epidemiology, and Laboratory Services, CDC.

All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.


* https://www.hhs.gov/about/agencies/iea/regional-offices/index.html

https://www.cdc.gov/nssp/overview.html

§ ESSENCE is a secure, integrated web-based application that allows application of custom and standardized analytic queries to identify, evaluate, share, and store syndromic surveillance data.

The Northeast region includes HHS Region 1 (Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont), HHS Region 2 (New Jersey and New York), and HHS Region 3 (District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia); the Southeast region includes HHS Region 4 (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee); the South Central region includes HHS Region 6 (Arkansas, Louisiana, New Mexico, and Texas); the Midwest region includes HHS Region 5 (Indiana, Illinois, Michigan, Minnesota, Ohio, and Wisconsin) and HHS Region 7 (Iowa, Kansas, Missouri, and Nebraska); the West region includes HHS Region 8 (Colorado, Montana, North Dakota, and Utah), HHS Region 9 (Arizona, California, and Nevada), and HHS Region 10 (Alaska, Idaho, Oregon, and Washington).

** https://www.cdc.gov/ticks/tickedvisits/index.html

†† https://www.cdc.gov/lyme/resources/FS-Guidance-for-Clinicians-Patients-after-TickBite-508.pdf

§§ https://www.cdc.gov/ticks/removing_a_tick.html

References

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TABLE. Cumulative number and incidence of emergency department (ED) visits for tick bites, by demographic factors, region, and month — National Syndromic Surveillance Program, United States, 2017–2019Return to your place in the text
Characteristic 2017 2018 2019 Cumulative average, 2017–2019
No. of tick bite ED visits* Total no. of ED visits Incidence§ of tick bite visits No. of tick bite ED visits* Total no. of ED visits Incidence§ of tick bite visits No. of tick bite ED visits* Total no. of ED visits Incidence§ of tick bite visits No. of tick bite ED visits* Total no. of ED visits Incidence§ of tick bite visits
Total 50,158 90,940,257 55 44,561 104,527,637 43 54,645 110,980,103 49 49,788 102,149,332 49
Sex
Male 28,678 39,785,212 72 24,917 46,382,359 54 30,846 49,519,825 62 28,147 45,229,132 63
Female 21,480 49,777,365 43 19,644 57,805,649 34 23,799 61,273,383 39 21,641 56,285,466 39
Age group, yrs
0–9 10,720 10,704,916 100 9,196 12,057,058 76 10,511 12,886,736 82 10,142 11,882,903 86
10–19 4,143 8,243,147 50 3,527 9,246,155 38 4,135 9,865,868 42 3,935 9,118,390 43
20–29 4,691 13,764,651 34 4,118 15,512,091 27 4,822 16,163,531 30 4,544 15,146,758 30
30–39 5,216 12,357,259 42 4,752 14,274,053 33 5,542 15,206,138 36 5,170 13,945,817 37
40–49 5,010 10,539,127 48 4,508 12,111,360 37 5,641 12,792,555 44 5,053 11,814,347 43
50–59 6,780 11,356,661 60 6,005 13,044,008 46 7,407 13,686,328 54 6,731 12,695,666 53
60–69 6,634 9,315,019 71 5,797 11,100,812 52 7,888 12,097,594 65 6,773 10,837,808 63
70–79 5,043 7,101,448 71 4,764 8,604,464 55 6,251 9,499,166 66 5,353 8,401,693 64
≥80 1,921 6,406,677 30 1,894 7,552,911 25 2,448 8,158,639 30 2,088 7,372,742 28
HHS region
1 12,347 4,067,333 304 10,419 6,237,317 167 15,930 6,941,317 229 12,899 5,748,656 233
2 10,279 10,941,507 94 7,358 11,634,469 63 9,524 12,004,088 79 9,054 11,526,688 79
3 10,634 10,992,838 97 8,309 11,403,157 73 9,220 12,055,553 76 9,388 11,483,849 82
4 7,825 27,908,048 28 8,047 30,030,851 27 8,294 30,692,825 27 8,055 29,543,908 27
5 5,174 15,998,559 32 5,977 20,329,466 29 7,029 20,833,532 34 6,060 19,053,852 32
6 934 6,064,208 15 899 8,297,951 11 942 10,087,091 9 925 8,149,750 12
7 1,852 4,029,845 46 1,742 4,070,726 43 1,722 4,225,766 41 1,772 4,108,779 43
8 294 2,217,989 13 290 2,309,572 13 334 2,517,931 13 306 2,348,497 13
9 693 5,569,146 12 733 6,418,490 11 869 6,789,059 13 765 6,258,898 12
10 126 1,773,107 7 787 3,795,681 21 781 4,833,260 16 565 3,467,349 15
Region**
Northeast 33,260 26,001,678 128 26,086 29,274,943 89 34,674 31,000,958 112 31,340 28,759,193 110
Midwest 7,825 20,028,404 39 8,047 24,400,192 33 8,751 25,059,298 35 8,208 23,162,631 36
Southeast 7,026 27,908,048 25 7,719 30,030,851 26 8,294 30,692,825 27 7,680 29,543,908 26
South Central 934 6,064,208 15 899 8,297,951 11 942 10,087,091 9 925 8,149,750 12
West 1,113 9,560,242 12 1,810 12,523,743 14 1,984 14,140,250 14 1,636 12,074,745 13
Month
January 545 7,492,932 7 373 9,270,005 4 481 9,046,380 5 466 8,603,106 6
February 983 6,829,363 14 961 8,446,446 11 463 8,506,546 5 802 7,927,452 10
March 1,428 7,441,914 19 1,266 8,662,761 15 1,334 9,457,533 14 1,343 8,520,736 16
April 6,678 7,134,015 94 4,344 8,427,314 52 7,824 9,045,045 87 6,282 8,202,125 77
May 10,934 7,421,685 147 12,889 8,835,952 146 12,965 9,439,181 137 12,263 8,565,606 144
June 9,476 7,017,227 135 9,413 8,376,279 112 11,027 8,897,334 124 9,972 8,096,947 124
July 5,849 7,238,783 81 5,353 8,711,041 61 6,316 9,305,038 68 5,839 8,418,287 70
August 2,471 7,838,505 32 2,812 8,834,930 32 2,903 9,278,326 31 2,729 8,650,587 32
September 1,293 7,944,542 16 1,640 8,770,367 19 1,879 9,390,582 20 1,604 8,701,830 18
October 5,252 8,199,536 64 2,753 8,913,738 31 5,424 9,343,509 58 4,476 8,818,928 51
November 4,195 7,961,834 53 2,113 8,341,256 25 3,101 9,166,370 34 3,136 8,489,820 37
December 1,054 8,419,921 13 644 8,937,591 7 928 10,104,817 9 875 9,154,110 10

Abbreviation: HHS = U.S. Department of Health and Human Services.
* Tick ED visits were identified by the CDC Tick Bite syndrome query (https://knowledgerepository.syndromicsurveillance.org/tick-bites-centers-disease-control-and-prevention).
Totals by category might not sum to overall total counts because of missing data in some categories.
§ Per 100,000 total ED visits.
HHS Region 1 (Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont), HHS Region 2 (New Jersey and New York), HHS Region 3 (District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia), HHS Region 4 (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee), HHS Region 6 (Arkansas, Louisiana, New Mexico, and Texas), HHS Region 5 (Indiana, Illinois, Michigan, Minnesota, Ohio, and Wisconsin), HHS Region 7 (Iowa, Kansas, Missouri, and Nebraska), HHS Region 8 (Colorado, Montana, North Dakota, and Utah), HHS Region 9 (Arizona, California, and Nevada), and HHS Region 10 (Alaska, Idaho, Oregon, and Washington).
** The Northeast region includes HHS Region 1 (Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont), HHS Region 2 (New Jersey and New York), and HHS Region 3 (District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia); the Southeast region includes HHS Region 4 (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee); the South Central region includes HHS Region 6 (Arkansas, Louisiana, New Mexico, and Texas); the Midwest region includes HHS Region 5 (Indiana, Illinois, Michigan, Minnesota, Ohio, and Wisconsin) and HHS Region 7 (Iowa, Kansas, Missouri, and Nebraska); the West region includes HHS Region 8 (Colorado, Montana, North Dakota, and Utah), HHS Region 9 (Arizona, California, and Nevada), and HHS Region 10 (Alaska, Idaho, Oregon, and Washington).

Return to your place in the textFIGURE. Emergency department (ED) visits for tick bites, by month — National Syndromic Surveillance Program, United States, 2017–2019
The figure is a bar chart showing the number of emergency department visits for tick bites by month in the United States during 2017–2019 according to the National Syndromic Surveillance Program.

Suggested citation for this article: Marx GE, Spillane M, Beck A, Stein Z, Powell AK, Hinckley AF. Emergency Department Visits for Tick Bites — United States, January 2017–December 2019 . MMWR Morb Mortal Wkly Rep 2021;70:612–616. DOI: http://dx.doi.org/10.15585/mmwr.mm7017a2.

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