For personal use only. Not to be reproduced without permission of The Lancet. 144 THE LANCET • Vol 357 • January 13, 2001 CORRESPONDENCE 3 Swaminathan R. Major P, Snieder H, Spector T. Serum creatinine and fat-free mass (lean body mass). Clin Chem 2000; 46: 19695–96. 4 Whitfield JB, Martin NG. The effects of inheritance on constituents of plasma: a twin study on some biochemical variables. Ann Clin Biochem 1984; 21: 176–83. colleagues have misplaced a decimal point in their per-act infectivity estimates; they assumed a per-act infectivity of 0·01 and 0·02 based on a reference that reported a per-act infectivity of 0·001 and 0·002. The estimate of ten cases prevented for every 100 people counselled (table 3) suggests that the incidence without intervention must be more than 10%. If so, we would expect the prevalence in the health information (control) group to increase by 5·8% (to 25·8%) during the 7 months before their first test. This change seems unlikely given the lack of difference in HIV-1 prevalence between the VCT group at baseline and the health information group measured at 7 months (table). Labour costs per client seem high and were almost 50% of the total costs (Kenya US$26.65, and Tanzania $28.93). The income per person in Kenya ($350) and Tanzania ($220; www.worldbank.org/data.countrydata. html accessed on Jan 8, 2001) suggest a lower labour cost. A study from Zambia (income per person $330) reported a total cost of $8 per person after counselling. 5 Information on the average hourly wage and time taken for counselling and testing would be helpful for comparisons with past and future studies. We believe that VCT is an important HIV-1 prevention intervention. Antiretroviral therapy, control of sexually transmitted diseases, and prevention of perinatal transmission are also important. Cost-benefit analyses can help efficiently allocate scarce prevention resources. These analyses always use assumptions and estimates based on the best available data. Future analyses can build on the foundation set by Sweat and colleagues, but, without details on the derivation of their estimates we cannot assess the strength of this foundation. *Beena Varghese, Thomas A Peterman, Constance Mugalla Division of HIV/AIDS Prevention, MS E-46, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA (e-mail: bav7@cdc.gov) 1 Sweat M, Gregorich S, Sangima G, et al. Cost-effectiveness of voluntary HIV-1 counselling and testing in reducing sexual transmission of HIV-1 in Kenya and Tanzania. Lancet 2000; 356: 113–21. 2 The Voluntary HIV-1 Counseling and Testing Efficacy Study Group. Efficacy of voluntary HIV-1 counselling and testing in individuals and couples in Kenya, Tanzania, and Trinidad: a randomised trial. Lancet 2000; 356: 103–12. 3 Allen S, Serufilira A, Bogaerts J, et al. Confidential HIV testing and condom promotion in Africa. Impact on HIV and gonorrhoea rates. JAMA 1992; 268: 3338–43. 4 Quinn TC, Wawer MJ, Sewankambo N, et al. Viral load and heterosexual transmission of human immunodeficiency virus type. N Engl J Med 2000; 342: 921–29. 5 McKenna SL, Muyinda GK, Roth D, et al. Rapid HIV testing and counseling for voluntary testing centers in Africa. AIDS 1997; 11 (suppl 1): 5103–10. Authors’ reply Sir—Beena Varghese and colleagues raise concerns over the specification of model parameters referenced in our analysis, citing “many” references we made to the main outcomes paper that they cannot find, leading to a lack of detail in the presentation of our assumptions. However, our cost- effectiveness paper refers only once to the main outcomes paper, for a review of the design of the larger study. Varghese and colleagues also raise doubts over the veracity of the findings because other studies of the behavioural impact of HIV-1 VCT yielded different outcomes. We urge caution in interpreting comparisons to the studies they cite, especially since the studies were done in different countries, were targeted to childbearing women, used different measures of condom use, and were done 7–8 years ago. The people who participated in our study independently sought out VCT and were probably more ready to make behavioural changes than the childbearing women in W L Heyward and colleagues’ 1993 study in Zaire (now the Democratic Republic of Congo) and S Allen and colleagues’ 1992 study in Rwanda. Moreover, comparisons made by Varghese between our report on the efficacy of VCT, and that on the cost-effectiveness of VCT are not parallel, since the main paper includes data from Trinidad, and the cost-effectiveness paper is limited to the African sites. For the infectivity parameter, in our original analysis we adjusted the parameter for HIV-1 transmission probability per sex act based on the high rate of sexually transmitted infection, and included a sensitivity analysis to account for variation in this parameter. We have previously reported on an expanded sensitivity analysis of the transmission probability parameter. 1 That analysis showed that even with the lower per-contact HIV-1 transmission probability, as suggested by Varghese and colleagues, VCT was shown to still be cost-effective by international standards. The impact on the cost-per disability-adjusted life year saved from using this upper bound value for the per-act probability of HIV-1 Voluntary counselling and testing for HIV-1 Sir—Michael Sweat and colleagues (July 8, p 113) 1 make an important contribution to the understanding of the role of voluntary counselling and testing (VCT) in Africa. We believe that many people will use variables from this study to estimate costs and effectiveness in other regions when relevant local parameters are not available. Many of Sweat’s efficacy parameters are attributed to the accompanying paper by the Voluntary HIV-1 Counseling and Testing Efficacy Study Group (July 8, p 103) 2 but we cannot find them there. We would like to know how the investigators derived their estimates because some costs and benefits seem high compared with those from previous studies. Sweat and colleagues suggest that condom use per act after VCT increased to 83–88% (shown in their table 1). We can find no information on per-act condom use in the accompanying paper, but at 12 months, 196 men reported intercourse with a main partner and 125 (64%) reported unprotected intercourse (a decrease from 79% at baseline). Another study found much less condom use per year after testing and counselling intervention. 3 The estimated rates of HIV transmission (0·0189 in Kenya and 0·0172 in Tanzania) suggest that 64% of the uninfected partners of infected people would acquire infection after 54 sex acts (the average number of sex-acts per year). The Rakai study reported transmission among discordant couples to be 12% per year and genital-ulcer disease increased this transmission to 13·7% per year. 4 It looks like Sweat and Country VCT at Health baseline information at 7 months Kenya Total number tested 716 571 Number positive 146 (20·4%) 100 (17·5%) Tanzania Total number tested 664 439 Number positive 132 (20%) 88 (20%) HIV-1 prevalence at baseline in VCT group and at 7 months in health information group