Table 2.
Subgroup analysis: meta-analytic pooled per-act HIV-1 transmission probability estimates for URAI and UIAI stratified by population subgroup (heterosexual and MSM), study design (retrospective-partner and prospective cohort of individuals) and plausible extent of ART use by sexual partners (0% versus >0%).
| Estimate type | Pooled estimate, % (95%CI) |
Pa | I2,b, (%) | N | References | p-valuea |
|---|---|---|---|---|---|---|
| URAI | ||||||
| Gender | ||||||
| Women | 3.38 (1.85-4.91) | 1.000 | 0.0% | 1 | 20 | |
| MSM | 0.75 (0.56-0.98) | 0.278 | <0.1% | 4 | 7, 8, 19c | p<0.0001 |
| Study design | ||||||
| Retrospective-partner | 2.56 (1.20-4.42) | 0.1296 | 56.5% | 2 | 19, 20 | |
| Prospective cohort of individuals | 0.71 (0.51-0.93) | 0.722 | 0.0% | 3 | 7, 8c | p<0.0001 |
| Plausible extent of ART use by sexual partners | ||||||
| 0% | 1.67 (0.44-3.67) | <0.0001 | 87.6% | 3 | 8, 19, 20d | |
| >0% | 0.75 (0.52–1.03) | 0.650 | 0.0% | 2 | 7, 8d | p=0.537 |
| Pooled estimate | 1.25 (0.55-2.23) | 0.0002 | 87.3% | 5 | 7, 8, 19, 20c | |
| UIAIe | ||||||
| Plausible extent of ART use by sexual partners | ||||||
| 0% | 0.14 (0.04-0.29) | 1.000 | 0.0% | 1 | 8 | |
| >0% | 0.18 (0.09-0.31) | 0.604 | 0.0% | 2 | 7, 8c | P=0.955 |
| Pooled estimate | 0.17 (0.09-0.26) | 0.7716 | 0.0% | 3 | 7, 8c | |
ART – antiretroviral treatment; N – number of study estimates; NA – not applicable; P – P-value; Q – heterogeneity statistic; UIAI – unprotected insertive anal intercourse; URAI – unprotected receptive anal intercourse.
“P” is the p-value for heterogeneity of the pooled estimate; “p-value” is the metaregression p-value defining the significance of the difference in pooled estimates between the two subgroups.
I2 is calculated as described in Higgins et al33. I2 lies between 0 and 100%; 0% indicates no observed heterogeneity and larger values show increasing heterogeneity.
Two URAI and UIAI estimates were provided by Scott et al8, using data from studies conducted in the pre-ART and early ART eras.
Scott et al’s8 pre-ART estimates are classed as likely 0% ART use; its early ART estimates are classed as >0% use.
All UIAI study estimates used data from prospective cohorts of individuals from MSM populations and so subgroup analysis could not be conducted gender or design.