An index to examine the sexual HIV risk of psychiatric service users based on sexual partners.

Numerous studies report higher HIV infection rates among psychiatric patients than in the general population.1 Relative to other HIV-affected populations, they have higher rates of HIV-related risk behaviors in fewer sexual occasions, including multiple partners, partners of unknown or positive HIV status, sex in exchange for money, shelter or goods, and low condom use rates.2 We present a new HIV risk index (RI)3 that takes into account differential risk associated with these factors.

Anal/vaginal receptive sex is riskier than insertive practices. Sex acts with partners of unknown/positive HIV status are riskier than those with HIV-negative partners, regardless of partner type.4 Lastly, sex acts with steady, casual, and exchange partners are associated with different HIV risk.5

Our RI assigns differential risk to each sex act and sums risk across sex acts. The differential risk consists of three risk coefficients: 1) partner (type and HIV status); 2) vaginal sex (insertive or receptive) per sex occasion; and 3) anal sex (insertive or receptive) per sex occasion. Risk coefficients for vaginal/anal directionality are based on CDC transmission risk values,6 while coefficients proposed for partner type were determined on the basis of expert opinion and face validity (Table 1).

Table 1

Risk coefficients by sex partner type and HIV status, sex occasions

Sex partner RC
Partner type*/HIV status	Heterosexual	MSM
Steady
Positive	1.00	1.00
Negative	0.01	0.01
Unknown	0.50	0.50
Casual		1.00
Positive	1.00
Negative	0.10	0.10
Unknown	0.75	0.90
Exchange	1.00	1.00
Positive
Negative	0.25	0.25
Unknown	0.90	0.90
Sex occasions RC †
	Vaginal-RC	Anal-RC
Receptive	0.08	1.38
Insertive	0.04	0.11

RI formula: RIn (Partner N) = RC [Partner type and HIV status]. *(RC[vaginal sex]. *number of condomless vaginal acts + RC[anal sex]. *number of condomless anal acts)

MSM = men who have sex with men; RC = risk coefficient; RI = risk index.

Steady partner: someone participants think of as a steady or main partner (spouse, girlfriend/boyfriend, lover, fiancée); casual partner: someone participants had sex with for love or fun, but did not think of as a main or steady partner; exchange partner: someone participants had sex with in exchange for something (money, drugs, alcohol, cigarettes, a place to sleep), whether the transaction was clearly negotiated or implied.

Sex occasions risk coefficients are based on epidemiological data provided by CDC.6

RI is estimated for each sex partner (RIn); the sum of all RIn corresponds to the total RI score. We provide three examples to demonstrate the new RI in comparison to focusing only on condomless sex proportions.

Example 1. A man had four anal sex acts, one insertive and three receptive, all condomless, with a casual male HIV-unknown partner. Taking into account the three risk coefficients, this person would have an RI = 0.90*(0.11*1+1.38*3) = 3.83. Based solely on the proportion of condomless sex occasions, this person’s risk would be classified as 100%.

Example 2. A man had three vaginally insertive acts, all condomless, with a casual HIV-negative partner. This person would have an RI = 0.10*(0.04*3) = 0.01. His risk classification based on the proportion of condomless sex occasions is 100%, which would not distinguish him meaningfully from the man in Example 1.

Example 3. A woman had sex with two male partners, steady HIV-negative and exchange HIV-unknown. The one sex occasion with the steady partner was condomless; with the exchange partner, she had seven sex occasions, of which one was condomless vaginal and three were condomless anal (total sex occasions = 8; condomless sex occasions = 5). Thus, RI1 (Partner 1) = 0.01*(0.08*1) = 0.001; RI2 (Partner 2) = 0.90*(0.01*1+1.38*3) = 3.74; RITotal = 0.001+3.74 = 3.74. The proportion of condomless sex occasions would be 62.5%. Relative to Example 1, the RI shows this person’s risk approximating his, though the proportion of condomless occasions shows her to be at considerably less risk.

Using our RI, possible misclassifications of risk based solely on the proportion of condomless sex occasions were identified. RI offers greater precision in estimating risk within psychiatric and potentially other populations now that Brazil is considering pre-exposure prophylaxis (PrEP – PrEPBrasil.com.br) for those at high risk. Additional behavioral and infection rate data are needed to further differentiate and validate high risk.

Disclosure

The authors report no conflicts of interest.