Risk of HIV transmission by healthcare workers - a systematic review.

Background: Occupational HIV infection among healthcare workers (HCWs) has declined markedly in high-income countries as a result of improved infection prevention and control, safety-engineered devices, and the widespread availability of antiretroviral post-exposure prophylaxis. However, the risk of HIV transmission from infected HCWs to patients remains incompletely defined. Methods: We conducted a systematic review of published studies reporting either documented HIV transmission events or the absence of transmission (look-back investigations) from HIV-infected HCWs to patients. In accordance with PRISMA guidelines, MEDLINE and Google Scholar were searched for relevant publications up to September 2025. For look-back studies with zero observed transmissions, exact binomial CIs were calculated. Pre-specified sensitivity analyses were performed to quantify statistical uncertainty arising from incomplete follow-up. Results: Of 222 records identified, 23 studies from five countries met the inclusion criteria. Direct provider-to-patient HIV transmission was documented from four source HCWs, three of whom performed exposure-prone procedures, resulting in a total of eight infected patients. The Florida dental cluster accounted for five molecularly confirmed transmissions among 1,100 tested exposed patients, corresponding to an estimated transmission probability of 0.45% (95% exact Clopper-Pearson confidence interval [CI], 0.15-1.06%), equivalent to approximately one transmission per 676 to 95 treated patients. Another single-case transmission investigation reported a lower estimated risk, with an upper confidence bound below 0.6% (approximately one transmission per 177 procedures). Two additional probable transmission events were reported without systematic testing of other exposed patients.Sixteen look-back studies comprising 32,899 potentially exposed patients, of whom 12,924 (39.3%) underwent HIV testing, identified no HCW-to-patient transmission. In the main analyses, two-sided exact 95% CIs yielded upper transmission risk estimates ranging from 0.16% to 8.60%, largely driven by the number of patients tested. To address incomplete follow-up and major methodological biases, sensitivity analyses assuming one undetected transmission among all exposed patients were performed. Under these deliberately conservative assumptions, upper confidence limits ranged from 0.07% to 6.17%, with the majority of studies remaining below 0.5%, corresponding to fewer than one transmission per 200 exposed patients. Conclusions: With the exception of a very small number of documented provider-to-patient transmission events, the available evidence indicates that even under pessimistic assumptions the maximum plausible risk of HCW-to-patient HIV transmission remains very low. These findings support the development of clear, evidence-based national guidelines for the management of HCWs living with HIV.