Christopher Brown

To determine the accuracy and cost efficiency of pooling sera prior to HIV-1 testing, sera from 8,000 Kinshasa factory workers and their spouses were screened individually (2.44% seropositive) and in 800 pools of 10 sera each. There were no false-negative or false-positive pools, resulting in a calculated seroprevalence estimate of 2.42%. Further testing of all sera in positive pools can identify HIV-positive individuals. These applications were modeled to compare the cost-efficiency of pooling with individual testing under different conditions. The results suggest that pooling provides an alternative test format for use in both developing and industrialized countries when the seroprevalence and/or the marginal cost of obtaining a sample are sufficiently low. For our cohort, testing only the pools for seroprevalence estimation resulted in a 78% cost saving compared with individual testing; pooling with subsequent identification of individual seropositives represented a 56% cost reduction.

Persistent diarrhea is a prominent feature of the acquired immunodeficiency syndrome in adults, but its cause and its effect on children with human immunodeficiency virus (HIV) infection are largely unknown, particularly in Africa. We studied a birth cohort of 429 infants born to HIV-positive or HIV-negative mothers in Zaire to determine the incidence of acute, recurrent (> or = 2 episodes), and persistent (> or = 14 days) diarrhea; outcome; and risk factors. Of the 238 infants whose mothers were HIV-positive, 53 were infected, 139 were uninfected, and the HIV status of 46 could not be determined. As compared with uninfected infants, infected infants had higher incidence rates for acute diarrhea (170 vs. 100 episodes per 100 child-years, P = 0.003), recurrent diarrhea (21 vs. 11, P = 0.12), and persistent diarrhea (19 vs. 4, P < 0.003). Persistent diarrhea developed in 11 HIV-infected infants; all but 1 died. It also developed in 19 uninfected infants; all but 1 survived. The prevalence of stool pathogens was similar in the two groups. In a multivariate model, persistent diarrhea in an infant was independently associated with symptomatic HIV type 1 infection in the mother (relative hazard, 1.5; P = 0.08). The incidence of persistent diarrhea in the uninfected infants of seropositive mothers was nearly double that in the uninfected infants of seronegative mothers (4.9 vs. 2.7 episodes per 100 child-years), and the risk increased if the mother died (relative hazard, 10.4). Significant growth impairment and severe immunosuppression occurred in the six to eight weeks before the onset of persistent diarrhea. In Zaire, infants with HIV infection have an 11-fold increased risk of death from diarrhea, largely persistent diarrhea, which is often preceded by recurrent episodes of acute diarrhea, malnutrition, or immunosuppression. Illness and death of the mother increase that risk, even among her uninfected infants.

Multiple gaze control capabilities are coordinated using predictive methods. Internal models of state allow smooth interaction of multivariable, multirate controls. The problem of rapid gaze shift in a simulated robotic system illustrates several styles of control interaction.