As for the influence of CCR2-CCR5 alleles or haplotypes on transmission and acquisition of infection, the highly significant deviation of the distribution of haplotypes from HWE among the index, but not the exposed partners, was strong evidence of a selective effect, and the differential deviation of the seroconverters, but not the persistently seronegatives, corroborated the difference. The gene discussed is CCR2; the disease is infection.