An incremental cost-utility ratio was calculated to combine the costs and benefits of the interventions under evaluation. However, in the base-case, the costs and benefits were not combined because the intervention (rapid test followed by prophylaxis) dominated the option of no intervention, which was both more expensive and less effective (fewer HIV cases prevented).
The analysis of alternative scenarios suggested that nevirapine prophylaxis would be preferred over zidovudine if the relative risk reduction of transmission with nevirapine prophylaxis was at least 0.61. Prophylactic administration to both mother and infant of either nevirapine or lamivudine, in addition to zidovudine, required that the combination be only minimally more effective in comparison with zidovudine monotherapy (relative risk reduction about 0.001 - 0.002 greater) to save additional costs.
With respect to the rapid test, empiric nevirapine therapy would be the preferred strategy over no intervention when rapid testing was not available, the acceptance rate of rapid HIV testing and treatment was 0.68, or the relative risk reduction with nevirapine prophylaxis were somewhat better than with zidovudine (relative risk reduction 0.71 for nevirapine compared with 0.62 for zidovudine prophylaxis). It would also be preferred if all infants were not ruled out for HIV by HIV polymerase chain reaction tests.
The sensitivity analysis showed that the results of the base-case were, in general, quite robust to variations in the base-case model inputs. Variable values had to be relatively extreme to result in the intervention being not cost-effective.
The threshold analysis suggested that the intervention was cost neutral when:
the acceptance rate of the rapid test was 0.26;
the proportion of women delivering before treatment was effective was 0.70;
the prevalence of HIV in women without prenatal care was 2/1,000;
the relative risk reduction in vertical HIV transmission was 0.25; or
the additional cost associated with earlier HIV treatment (compared with delayed treatment) was $13,000.
Nevertheless, the intervention remained cost-effective (i.e. it had a cost per QALY below the threshold of $50,000 per QALY).