An analytical study is conducted of the properties of statistical tests to detect linkage between a disease locus and a very polymorphic marker locus when data on sib pairs are available. In most instances the most powerful test is the test based on the mean number of marker alleles shared identical by descent by the two members of a sib pair, and the most efficient sampling strategy is almost always to sample only pairs with both sibs affected. We show it is valid to use the information from all possible sib pairs as though they came from separate families when data on sibships of size three or larger are available, though more power may be obtained if different weights are given to the different sibship sizes.
To assess the risk of nosocomial transmission of human T-cell lymphotropic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV), we prospectively evaluated a cohort of 531 health care workers. One hundred fifty of these employees reported percutaneous or mucous membrane exposures to blood or body fluids from a patient with the acquired immunodeficiency syndrome (AIDS) during the treatment of 238 such patients since 1981. None of these 150 employees had serologic evidence of HTLV-III/LAV infection on follow-up from 6 to 46 months after exposure. Of the 150, 46 were studied immunologically and 29 had lymphocytes cultured for HTLV-III/LAV. Results of all studies were normal. Of the 531 employees, 3 (0.56%) had serologic evidence of HTLV-III/LAV infection. All were seropositive at the time of study entry; none reported adverse nosocomial exposures. All acknowledged membership in one or more established risk groups for AIDS. This study provides strong evidence that the risk of nosocomial transmission of HTLV-III/LAV is extremely low.
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