Under-recognized yet Clinically Relevant: A Hospital-based Study of Toxoplasma gondii Seropositivity in Bihar, India

Toxoplasma gondii is a globally prevalent protozoan parasite with marked regional variation in seroprevalence and clinical expression, yet data from eastern India, particularly Bihar, remain scarce. This retrospective cross-sectional study evaluated the serological positivity among clinically suspected patients and clinical spectrum of toxoplasmosis in Bihar using laboratory and clinical data from a tertiary-care centre in Patna between September 2021 and July 2025. A total of 2,014 serum samples were tested for T. gondii IgM and IgG antibodies using chemiluminescent immunoassay, and serological results were correlated with demographic, geographic, and clinical information. Overall serological positivity among clinically suspected patients was 4.86%, comprising 3.62% IgG-reactive cases, 1.1% IgM-reactive cases, and 0.14% with dual IgM-IgG positivity. Seropositivity increased with age and was more common in males. Geographic mapping demonstrated marked heterogeneity, with Patna contributing 45.9% of all seropositive cases, followed by smaller clusters in Buxar, Gaya, and Samastipur. Referrals originated predominantly from Pediatrics and Ophthalmology (31.6% each), followed by Obstetrics and Gynaecology, ENT, and Medicine. Among seropositive patients with available clinical data, ocular toxoplasmosis was the most frequent presentation (29.3%), largely manifesting as cataract and glaucoma. Sensorineural hearing loss accounted for 24.4% of cases, while adverse obstetric outcomes comprised 19.5%. Central nervous system involvement included meningoencephalitis, hydrocephalus, epileptic spasms, and cranial nerve palsies. Hepatic and pulmonary manifestations, including liver abscess and pneumonia, were also observed, reflecting a wide and atypical clinical spectrum. These findings demonstrate substantial clinical heterogeneity despite low seropositivity, underscoring the need for targeted diagnostic vigilance in endemic settings.