Methods: HIV screening is an effective prevention intervention because awareness of one's positive serostatus reduces the probability of transmission. We consider HIV transmissions occurring among inmates, and in the community after HIV-infected inmates are released. Our key outcome is cost per case of HIV averted. Intraprison HIV transmission rates were drawn from a study of HIV transmission in a state prison system of 45,000 male inmates. Transmission rates in the community are derived from HIV incidence among high-risk groups. Testing costs were collected from a multi-site evaluation of HIV testing in jails. We consider three HIV screening strategies in prison: at entry, upon release and annually during incarceration. We evaluate all eight combinations of these strategies, including no screening. We use Markov cohort simulation to model the movement of prisoners to and from the community, and evaluate costs and outcomes over 25 years. Costs and outcomes are discounted at 3% annually.

Results: Screening upon release averts 1904 infections at a cost of $5700 each compared with no screening. This option is less expensive and more effective than screening at entry only, and screening annually only. An additional 37 infections can be averted at a cost of $297,143 each by screening at entry and release compared with screening upon release only.

Table 1: Costs and outcomes of HIV screening strategies among incarcerated males (US$2004)

Screening strategy	Total cost	Total new HIV infections	% new infections in community	Incremental CE ratio ($/ infection averted)
No screening	$ 0	2,292	96%	n/a
Annual only	$22,631,568	1,121	93%	Dominated
Entry only	$11,134,559	435	85%	Dominated
Release only	$10,852,153	388	74%	$ 5,700
Release & annual	$33,388,756	363	79%	Dominated
Entry & annual	$33,658,446	359	82%	Dominated
Entry & release	$21,846,461	351	81%	$ 297,143
Entry, release & annual	$44,364,881	350	82%	$ 22,518,420

Conclusions/Implications: Screening prisoners upon their release is a cost-effective HIV prevention strategy. The majority of new infections occur in the community and screening upon release prevents the most infections in the community.