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To the Editor: Diagnosis of early Lyme disease, Borrelia burgdorferi infection, is difficult as Lyme associated symptoms are nonspecific. Erythema migrans (EM) is the only distinctive sign of early Lyme and it has been a useful diagnostic marker. However, EM is not as reliable a marker of Lyme as was thought1. Nonetheless, patients presenting with an EM-like lesion should still be treated for Lyme as the risks of antibiotic treatment are likely less than risks associated with untreated Lyme. Amblyomma americanum ticks have spread into Lyme endemic areas where Ixodes scapularis (vector of Borrelia burgdorferi), had been the dominant tick species, bringing Southern tick associated rash illness (STARI)2 into these areas. As EM and STARI lesions are indistinguishable in appearance2, the overlap between the two tick species in the Mid-Atlantic States, and more recently, Long Island NY, and Southern New England is causing diagnostic uncertainty. STARI should now be included in the differential diagnosis3 (Table 1) of EM-like skin lesions in these regions. Notably, this raises concerns regarding the validity of the conclusions drawn from studies that enrolled patients from these regions primarily based on clinician-diagnosed EM.

causing diagnostic uncertainty. STARI should now be included in the differential diagnosis3 (Table 1) of EM-like skin lesions in these regions. Notably, this raises concerns regarding the validity of the conclusions drawn from studies that enrolled patients from these regions primarily based on clinician-diagnosed EM. Determination that an EM-like skin lesion is truly Lyme EM and not STARI requires microbiologic proof (PCR or culture). PCR of EM skin biopsies is a method to confirm Borrelia burgdorferi infection with over 70% positivity in published studies4. As part of our ongoing research to improve early diagnostics, we have been using a modified version of the digital PCR5 to detect Borrelia burgdorferi DNA in skin biopsies of EM-like lesions obtained pretreatment to confirm Borrelia burgdorferi infection. In skin biopsy samples of EM-like skin lesions obtained in 2017–20 and in 2023–4 run concurrently, we found, here in the NY/NJ area, a change in the frequency of Borrelia burgdorferi PCR positivity in the 2017–20 seasons 56/71 (79%) compared to the 2023–4 seasons 1/18 (5.6%). Over the period, 2017 to 2023, A. americanum surpassed I. scapularis as the predominant tick species on Eastern Long Island.

run concurrently, we found, here in the NY/NJ area, a change in the frequency of Borrelia burgdorferi PCR positivity in the 2017–20 seasons 56/71 (79%) compared to the 2023–4 seasons 1/18 (5.6%). Over the period, 2017 to 2023, A. americanum surpassed I. scapularis as the predominant tick species on Eastern Long Island. The reduction of the rate of PCR positivity in EM-like lesions highlights that in areas where A. americanum ticks are present, EM-like lesions are not reliable as the primary entry criteria for patients enrolled in epidemiology, vaccine, treatment or outcome studies. In these areas, microbiologic confirmation may be needed to ensure the study population has Borrelia burgdorferi infection and to exclude non-Lyme disease processes. This is distinct from use of an EM-like lesion for clinical decisions.