Toxoplasma gondii screening and seroprevalence in Australasian deceased organ donors

Introduction: Donor-derived toxoplasmosis is a rare but potentially devastating complication of solid-organ transplantation. Latent infection persists predominantly in muscle tissue meaning heart transplantation confers the highest risk, particularly in uninfected individuals receiving a transplanted organ from a seropositive donor (D+/R–). Trimethoprim-sulfamethoxazole prophylaxis is highly effective at preventing Toxoplasma reactivation and mitigates clinical sequelae of donor-derived infection, however not all patients receive this. Prompted by a case of donor-derived cerebral toxoplasmosis following combined lung-kidney transplantation at our centre, we aimed to characterise toxoplasma screening practices and seroprevalence among Australasian deceased organ donors, and provide region-specific information to clinicians to aid risk-stratification of patients.
Methods: We performed a retrospective observational cohort study using deidentified data from the Australia and New Zealand Organ Donation (ANZOD) Registry, including all deceased organ donors between 1989 and 2024. Toxoplasma serostatus was determined by IgG testing at local laboratories. The proportion of donors tested annually, and the proportion of positive, negative and indeterminate test results were calculated. Categorical variables are presented as counts and percentages, and regional seroprevalence was compared using Fisher’s exact test.
Results: A total of 14,677 deceased organ donors were identified over the study period, of whom 4831 (33%) underwent toxoplasma serological testing (Figure 1). Donor testing changed substantially over time: the first recorded testing occurred in 2002 (1/252 donors, 0.4%), and the rate rose to 716/788 (91%) in 2024. Overall, 991/4831 (21%) donors were seropositive, 3761/4831 (78%) seronegative, and 79/4831 (2%) indeterminate. Seroprevalence remained stable over time, ranging from 17–23% from 2014 onwards (Figure 1). Significant regional variation was observed, ranging from 12% (7/58) in the Northern Territory to 37% (129/348) in New Zealand (p<0.001, Figure 2).

Conclusion: Approximately one in five Australasian deceased organ donors have latent toxoplasma infection, representing a risk for donor-derived infection in seronegative recipients. The proportion of donors being tested has increased to around 90% in recent years. Universal donor screening, robust prophylaxis strategies, and improved Australasian surveillance systems could help prevent donor-derived toxoplasmosis resulting in clinical illness in the future.