BACKGROUND: HIV incidence among people who inject drugs (PWID) in South Africa has never been estimated, yet it is essential for informing prevention efforts and tracking progress towards ending HIV/AIDS by 2030. We estimated HIV incidence and associated risk factors among PWID engaged with harm-reduction services in four provinces in South Africa.
METHODS: Programmatic data over April 2019–March 2022 were obtained from harm-reduction services funded by the Networking HIV and AIDS Community of South Africa (NACOSA), which serve PWID in four provinces (Gauteng, KwaZulu-Natal, Western Cape and Eastern Cape). At each visit, clients who were not known to be HIV-positive were offered HIV testing. They also self-reported socio-demographic characteristics, drug use patterns and uptake of harm-reduction services. HIV incidence was estimated using the person-time method among PWID at-risk of infection tested at least twice.
RESULTS: Data were available for 31,873 PWID, of whom 2,457 (7.7%) were initially HIV-negative and had =2 HIV tests, forming the sample for this study. At baseline, most were male (90.2%), black (72.2%), homeless or unstably housed (62.6%) and used heroin (97.3%). Median age was 30yrs and few (7.9%) ever received opioid agonist treatment (OAT). 300 (12.2%) PWID acquired HIV over 2190.2 person-years, resulting in an HIV incidence of 13.7/100 person years (95%CI: 12.2-15.3). The risk of HIV acquisition varied by province, being higher in Gauteng and KwaZulu-Natal compared to Western and Eastern Capes, and by age, being higher in younger relative to older PWID (Table). PWID who have received OAT and a greater number of harm-reduction packs had lower risks of HIV acquisition (Table).

Characteristic	Strata	HIV incidence (95%CI)	Incidence rate ratio (95% CI)	Characteristic	Strata	HIV incidence (95% CI)	Incidence rate ratio (95% CI)
Province	Gauteng	18.9 (16.5 - 21.6)	Ref.	Gender	Male	14.2 (12.6 - 15.9)	Ref.
	KwaZulu-Natal	17.1 (13.3 - 21.7)	0.9 (0.7 - 1.2)		Female	10.1 (6.7 - 14.8)	0.7 (0.5 - 1.1)
	Western Cape	3.4 (2.1 - 5.2)	0.2 (0.1 - 0.3)	Use of opioid substitution therapy	No, never	14.7 (13.2 - 16.6)	Ref.
	Eastern Cape	6.3 (3.2 - 11.2)	0.3 (0.2 - 0.6)		Yes, prior to the first HIV test	8.4 (2.1 - 22.9)	0.6 (0.1 - 1.7)
Age (years)	17-27	18.5 (15.2 - 22.2)	Ref.		Yes, following the first HIV test	3.8 (1.7 - 7.6)	0.3 (0.1 - 0.5)
	28-30	15.7 (12.3 - 19.8)	0.9 (0.6 - 1.2)	Number of harm-reduction packs received	0-2	17.5 (15.1-20.1)	Ref.
	31-35	13.7 (10.9 - 16.9)	0.7 (0.6 - 1.0)		3-5	10.3 (8.3-12.6)	0.6 (0.5 - 0.8)
	36-75	7.4 (5.4 - 9.9)	0.4 (0.3 - 0.6)		=6	8.7 (5.4 - 13.3)	0.5 (0.3 - 0.8)

CONCLUSIONS: Our results indicate that HIV incidence among PWID engaged with harm-reduction services in South Africa is very high and illustrate the value of using programmatic data to monitor the HIV epidemic in this vulnerable population. An urgent expansion of prevention services is needed.