Seasonal Variations in Human Toxoplasma Infection in Serbia

Background: Seasonal variations in the occurrence of toxoplasmosis have been studied only sporadically. We thus examined the seasonal distribution of acute toxoplasmosis in Serbia during a 4-year period (2004-2008). Materials and methods: A total of 391 consecutive symptomatic (recent lymphadenopathy) and 715 asymptomatic (women tested for obstetric reasons) patients were tested for Toxoplasma immunoglobulin G (IgG) (including IgG avidity) and IgM antibodies. The distribution of patients with acute infection, and of all patients from both groups, was analyzed for seasonality. In addition, factors (including undercooked meat consumption, contact with cats and with soil) possibly contributing to seasonality were analyzed in patients with acute infection (cases) matched by age, sex, and time (month and year) of infection (symptomatic) or presentation (asymptomatic) with seronegative patients (controls). Results: Acute toxoplasmosis was serologically (IgG avidity low, IgM positive) diagnosed in 39 (10.0%) symptomatic and 38 (5.3%) asymptomatic patients. In both groups, monthly distribution of acute infections showed significant (p< 0.0001) seasonality, which was related to the four seasons of the year (p< 0.0001). Importantly, the observed seasonality was not related to the distribution of all examined patients in either group (p< 0.001). In the symptomatic patients, acute infections occurred more often between October and March (p 0.0486). Although more asymptomatic acute infections were diagnosed between February and July (p 0.0037), low IgG avidity suggests that infection had occurred within the previous trimester (between November and April). Undercooked meat consumption was shown as a risk factor for symptomatic infection in the October-March period (odds ratio 7.67, 95% confidence interval 1.61-36.45). Conclusion: Seasonality patterns should be taken into account in the health education guidelines for the prevention of toxoplasmosis in pregnant women.