Background Sexual transmission is the fastest growing route of HIV transmission in China. Methods Cross-sectional study of 737 female sex workers (FSW) in Kaiyuan City, Yunnan Province, China from March-May 2006 to describe risk factors for HIV infection and to determine the commercial sex venues where FSWs were most at risk of being infected with or infecting others with HIV. Results Overall HIV prevalence was 10.3%, but prevalence varied with the sex venue with 25.8% of FSWs working on streets being HIV-positive and none of the FSWs working in night clubs. Adjusted odds ratios (OR) of HIV infection were 9.1 (95% CI: 4.67–17.55) for injection drug use; 3.3 (95% CI: 1.46–7.37) for non-injection illegal drug use; 2.7 (95% CI: 1.25–5.93) for duration of sex work ≥5 years; 2.2 (95% CI: 1.05–4.70) for infection with herpes simplex virus type 2; and 2.0 (95% CI: 1.12–3.47) for working at a higher risk entertainment venue. Although condom use was not a significant risk factor in the overall model, FSWs in lower risk venues who reported consistent use with clients had a 70% reduction in HIV infections (OR: 0.30; 95% CI: 0.12–0.90). Conclusions Illegal drug use, particularly with injection drugs, is the single greatest risk factor for HIV infection among FSWs in Kaiyuan City, China. FSWs working on the street or in temporary sublets, beauty salons or saunas are at particularly high risk for transmitting and being infected with HIV. HIV prevention efforts among FSWs should target illegal drug users and these other subgroups.

Some invasive hymenopteran social insects found new populations with very few reproductive individuals. This is despite the high cost of founder effects for such insects, which generally require heterozygosity at a single locus-the complementary sex determiner, csd-to develop as females. Individuals that are homozygous at csd develop as either infertile or subfertile diploid males or not at all. Furthermore, diploid males replace the female workers that are essential for colony function. Here we document how the Asian honey bee (Apis cerana) overcame the diploid male problem during its invasion of Australia. Natural selection prevented the loss of rare csd alleles due to genetic drift and corrected the skew in allele frequencies caused by founder effects to restore high average heterozygosity. Thus, balancing selection can alleviate the genetic load at csd imposed by severe bottlenecks, and so facilitate invasiveness.

The number and proportion of HIV/AIDS among older adults have increased in recent years. The hot spots showed movement from central to southern China. A focused intervention strategy targeting the older PLWHA is urgently required in China.

Objectives To assess the prevalence and risk factors of HIV among male clients of female sex workers in China. Methods Convenience sampling methods were used to recruit 315 clients using FSW-client and client-client networks. Subjects provided information on socio-demographic characteristics and sexual and drug behavior patterns. Blood samples were collected for HIV testing and urine samples for opiate testing. Results Overall HIV prevalence was 6.0%; among drug users it was 30.8%. 33.7% of respondents reported that they always use condoms in commercial sex and 63.5% that they used a condom in the last commercial sex episode. Drug use (OR: 6.1; 95% CI: 1.7–21.4) and lack of a regular sexual partner (OR: 6.3; 95% CI: 1.8–21.9) were significantly associated with HIV infection. Conclusions Clients of FSWs serve as potential bridges for HIV transmission from the high-risk FSWs to the low-risk general population, making them a key target for intervention. High HIV prevalence rates among clients in Kaiyuan is particularly alarming given their risk behavior patterns including high rates of partner exchange, low condom use rates, and drug using behaviors. Innovative interventions are needed to reduce the risk of HIV among clients and reduce the bridge of transmission to the general population.