**Background:** Tick-borne diseases are a growing public health concern in the northeastern United States, with Massachusetts being a high-risk area for Lyme disease, babesiosis, and anaplasmosis. While environmental tick collection studies provide data on vector density, they do not account for human behavior and exposure. Passive surveillance of human-biting ticks can fill this gap by capturing actual human-tick encounters. TickReport, a public outreach service at the University of Massachusetts Amherst, provides tick identification and pathogen testing to individuals. This study analyzed human-biting I. scapularis ticks submitted to TickReport from 2015–2019 in Massachusetts to examine patterns of pathogen-positive ticks over time and explore how socioeconomic factors influence tick submissions.
**Methods:** A total of 13,598 I. scapularis ticks submitted voluntarily from January 2015 through December 2019 with a reported Massachusetts exposure location were included. Ticks were morphologically identified and confirmed by molecular assays targeting the mitochondrial 16S rRNA and ITS genes. DNA was extracted and tested for B. burgdorferi s.l., B. miyamotoi, B. mayonii, B. microti, and A. phagocytophilum using multiplex TaqMan real-time PCR. Pathogen prevalence was calculated by life stage, month, year, county, and zip code tabulation area (ZCTA) with 95% confidence intervals. Annual trends were analyzed using the Mann-Kendall Test (p < 0.05). For socioeconomic analysis, negative binomial regression models examined associations between ZCTA-level variables (median household income, percentage white race, percentage high school education or less, population density, distance to TickReport lab, land use) and tick submissions per ZCTA. Boston-area ZCTAs were excluded a priori due to consistently low submissions despite wide socioeconomic variation.
**Key Results:** Of 13,598 ticks, 76.7% were adults (n=10,435), 21.6% nymphs (n=2,935), and 1.7% larvae (n=228). Men and women submitted similar numbers (6,743 vs. 6,701). 96.6% reported exposure location at ZCTA level, and 77.4% of exposures occurred in the same ZCTA as residence. No ticks were submitted from 11.1% (59/537) of Massachusetts ZCTAs. In adult ticks, pathogen prevalence was: B. burgdorferi 39.0% (95% CI: 38.1–39.9%), B. microti 8.1% (95% CI: 7.6–8.6%), A. phagocytophilum 7.6% (95% CI: 7.1–8.1%), and B. miyamotoi 2.0% (95% CI: 1.7–2.3%). In nymphs: B. burgdorferi 23.1% (95% CI: 21.6–24.7%), B. microti 6.4% (95% CI: 5.6–7.4%), A. phagocytophilum 4.9% (95% CI: 4.2–5.8%), and B. miyamotoi 1.3% (95% CI: 0.9–1.8%). No ticks were positive for B. mayonii. Combined, 41.5% (95% CI: 40.7–42.3%) were infected with at least one pathogen; 8.8% (95% CI: 8.3–9.3%) with more than one. Five adult ticks were positive for all four pathogens. No pathogen exhibited a significant linear trend over the study period. Exposure showed two seasonal peaks: spring/early summer (April–June) and fall (October–November). Nymphs showed a single peak in late spring/early summer. Compared to TickReport data from 2006–2013, B. burgdorferi prevalence increased from 29.6% to 35.0%, B. microti from 4.6% to 7.6%, and A. phagocytophilum from 1.8% to 6.9% of all ticks. Socioeconomic analysis (excluding Boston) showed that ZCTAs with higher percentage of white race were positively associated with tick submissions. Higher median household income and higher percentage with high school education or less were associated with fewer submissions. Longer distance to TickReport lab was positively associated with submissions (IRR = 1.003 per 1 km; 95% CI 1.002–1.006). After removing the influential point (Amherst, 01002), percentage white race became significant even with land use included, and median household income became insignificant. When Boston was included, population density became the most significant factor.
**Clinical Implications:** Passive surveillance of human-biting ticks provides critical data for monitoring tick-borne disease risk and detecting geographic expansion of pathogens. The finding that B. microti has expanded from Cape Cod and the islands to all Massachusetts counties except Suffolk County has direct implications for clinical diagnosis—clinicians should consider babesiosis even in inland patients. The high rate of co-infection (8.8% with more than one pathogen) underscores the need for testing patients with tick-borne illness for multiple pathogens simultaneously. The association of tick submissions with higher education levels and white race, even after accounting for land use, suggests that passive surveillance data may underestimate risk in underserved populations. Public health interventions should address these disparities, potentially through subsidized testing programs or insurance coverage, to ensure equitable surveillance and risk communication.