Background
Incident HIV infections during pregnancy and breastfeeding increase the risk of Mother to Child Transmission (MTCT) of HIV by as much as 18%. Zimbabwe registered an MTCT rate of 8.7% in 2020 against a <5% target. Seke District recorded the highest number of incident HIV infections among pregnant and lactating women (PLW) with 211 infections recorded in 2020. We investigated factors associated with incident HIV infection in PLW.

Methods
We conducted a 1:1 unmatched case-control study with 90 case-control pairs. A case was defined as any PLW aged ≥18 years who initially tested HIV negative on first antenatal care (ANC) booking but subsequently tested HIV positive on repeat tests during ANC visits or breastfeeding period up to 12 months of follow up between 31 July 2020 and 31 July 2021. Simple random sampling was used to recruit PLW from antenatal and post natal registers at health care facilities. Data were collected through an interviewer-administered questionnaire. Univariate, bivariate and logistic regression analysis was conducted at 95% Confidence Interval (CI).

Results
Being ‘single’ on marital status (aOR 3.2, 95 % CI 1.8–6.7), being in an age –disparate partnership/marriages (aOR 1.7, 95 % CI 1.59–2.6), having a history of an STI diagnosis (aOR 4.8, 95% CI 2.0–5.7) and having knowledge of partner’s HIV status (aOR 0.57, 95% CI 0.03 – 0.91) were independent factors associated with incident HIV infection in PLW. Overall knowledge for cases and controls on prevention of mother to child transmission of HIV was rated as good.

Conclusion
Prioritization of routine advocacy on benefits of couples' HIV testing, STI management and strengthening entrepreneurial and vocational training to promote financial independence for younger women is necessary to prevent incident HIV acquisition in PLW. We gave health education to PLW attending ante and post natal care on Pre-Exposure Prophylaxis as an option for HIV prevention.