Impact of hepatitis B immunisation as part of the EPI.

Since 1992, hepatitis B vaccine has been an integrated part of Thailand's expanded programme on immunisation (EPI). Based on the data from five representative provinces, we have evaluated its impact on the countrywide prevalence of HBV infection and carrier rate. The population studied comprised 400-488 healthy and immuno-competent, subjects per area. The subjects' ages ranged from 6 months to 18 years. We examined their sera for viral hepatitis markers using commercially available test kits and established the coverage rate of hepatitis B vaccination after its inclusion into the EPI to be 71.2-94.3%. The number of individuals undergoing the complete course of vaccinations had increased four-fold. Consequently, only 0.7% of the children born after the implementation of this the novel EPI strategy were HBV carriers.

Persistence of antibodies to the surface antigen of the hepatitis B virus (anti-HBs) in children subjected to the Expanded Programme on Immunization (EPI), including hepatitis-B vaccine, in Thailand.

Will hepatitis-B vaccine administered at birth, and at 2 and 6 months of age, as an integral part of Thailand's Expanded Programme on Immunization, provide long-term protection? In an attempt to answer this question, residents of five provinces (representing five distinct geographical areas of Thailand) who were aged 1-10 years and had received this course of vaccination were enrolled on a serological study. Each was tested, with ELISA, for the surface antigen of hepatitis B (HBsAg) and for antibodies against this antigen (anti-HBs) or against the core antigen (anti-HBc). Over all age-groups, the prevalences of HBsAg, anti-HBs and anti-HBc were 0.67%, 71.4% and 5.5%, respectively. Although the prevalence of anti-HBs decreased with age, it remained at 56%-65% among those aged 6-10 years. Between 2% and 17% of the subjects aged 1-9 years had high titres of anti-HBs. Based on these results, an additional booster, still a controversial issue, does not appear to be required in order to prevent infection with hepatitis B virus and thus permit the eventual eradication of chronic carriage and its fatal sequelae in Thailand.

Increasing susceptibility to HAV among members of the young generation in Thailand.

The prevalence of antibodies to hepatitis A virus was studied in 961 children and adolescents, randomly selected from five different provinces in Thailand (Chonburi, Lopburi, Udonthani, Nakhon Si Thammarat and Lopburi). The highest prevalence was found in Nakhon Si Thammarat, with 32.1 percent of those aged 10-14 years and 57.1 percent of those aged 15-18 years showing evidence of protective immunity. However, this high rate could be explained by an outbreak of hepatitis A in 1992. In the remaining four provinces, the pattern was typically age-related in that all individuals showed between zero and 13 percent antibody prevalence until reaching the 15-to-18-year age group where it increased to between 5.6 and 22.7 percent. The overall sero-prevalence among all age groups was 7.9 percent. Thus, the majority of the younger generation is susceptible to hepatitis A virus infection thereby enhancing the impact, should an outbreak occur. Preventive measures that might be taken are education aimed at better hygiene and sanitation, as well as vaccination of susceptible individuals within high-risk populations.

Feasibility of a preventive HIV-1 vaccine cohort among persons attending sexually transmitted disease clinics in Thailand.

Persons attending sexually transmitted disease clinics at three sites in Thailand were recruited to participate in a 1-year study of HIV-1 incidence. Between September 1995 and February 1996, 31% (371 of 1205) of eligible men and 24% (161 of 659) of eligible women agreed to participate. At enrollment, HIV-1 seropositivity was 3.8% among men and 2.5% among women. Follow-up of the 514 participants who were seronegative at baseline was 78% at the 12-month visit. During the study period, 53% of men reported 2 or more sexual partners, 31% reported sex with a commercial sex worker (CSW), and 33% with a casual partner. Of those visiting CSWs, 72% reported consistent condom use. Among women, 11% reported 2 or more sexual partners. Decreased HIV risk behaviors among men were observed during the study. Four incident infections occurred in men (1.4/100 person-years, 95% confidence interval [CI] = 0.4-3.6) and none among women. Based on the observed HIV-1 incidence, HIV vaccine efficacy trials in such populations would have to be larger than previously planned or more selective of high risk subgroups for recruitment.

PIP: Thailand is one of the few countries in which plans for HIV-1 vaccine efficacy trials are proceeding. The determination of cohort sample size for such trials depends upon the HIV-1 incidence among those who may enroll in the trials, participant retention, trial duration, and the frequency of risk behavior during the trial. The authors conducted a prospective cohort study of sexually transmitted disease (STD) clinic attendees at 3 sites in Thailand to determine whether a cohort in the population would be suitable for future HIV-1 vaccine efficacy trials. Between September 1995 and February 1996, 371 of 1205 (31%) eligible men and 161 of 659 (24%) eligible women agreed to participate in a 1-year study of HIV-1 incidence. At enrollment, 3.8% of the men and 2.5% of the women were infected with HIV-1. Almost all women and 54% of the men were married at the time of enrollment. 78% of the 514 participants who were seronegative at baseline were still being followed at the 12-month visit. During the study period, 53% of men reported having 2 or more sex partners, 31% reported having sex with a prostitute, and 33% with a casual partner. 72% of those frequenting prostitutes reported consistent condom use. 11% of women reported 2 or more sex partners. Decreased HIV risk behaviors among men were observed during the study. 4 incident infections occurred in men and none among the women. Based upon this observed HIV-1 infection incidence, HIV vaccine efficacy trials in such populations would have to be larger than previously planned or more selective of high-risk subgroups for recruitment.

Cost benefit analysis of Japanese encephalitis vaccination program in Thailand.

Using decision analysis, we estimated benefits, risks, and costs of implementing the Japanese encephalitis (JE) vaccination program in children aged 18 months and 6 years in Thailand. The costs for inclusion of JE vaccine into the routine immunization program at 18 months and 6 years are $2.16 and $3.68 per person, respectively. In the baseline model, the JE vaccination program will prevent 124 JE cases in the program for 18 months old children and 153 JE cases in the program for 6 years old children. The 18 month child program is more cost-effective than the 6 year child program. The cost-effectiveness ratio in the 18 month child program is $15,715 compared with $21,661 in the 6 year child program. The benefits of the JE vaccination program are the savings in treatment cost, disability care, and the future lifetime earnings from JE prevented. The 18 month child program will save $72,922 per one prevented JE compared with $66,197 in the 6 year child program. The JE vaccination program is cost-beneficial under the base-case assumption. Sensitivity analysis which alters various assumptions indicates that the JE vaccination program is worth implementing unless the incidence of JE is less than 3 per 100,000 population. Otherwise, the cost of vaccine has to be reduced.

Determinants of HIV infection among female commercial sex workers in northeastern Thailand: results from a longitudinal study.

Our objective was to estimate HIV seroconversion rates among commercial sex workers (CSWs) between 1990 and 1991 and to identify the behavioral, demographic, and reproductive determinants of these rates. This study has a prospective (n = 240 with 15 cases) and a cross-sectional component (n = 271 with 34 cases). In November 1990, HIV-negative female CSWs from 24 brothels in Khon Kaen city were interviewed and were followed prospectively for up to 1 year. In March, June, and September 1991, additional HIV-negative CSWs were enrolled and prospectively followed. HIV seroconversion rates were calculated, and the Cox regression model was used to estimate the relative risks of HIV seroconversion from demographic, sexual practice, and reproductive factors, adjusted for the effects of the others, among 232 of the 240 without missing data. Seroprevalence rates were also calculated for the 271 participants enrolled between March and December 1991, and relative risks of HIV seroprevalence were calculated for demographic, sexual practice, and reproductive risk factors among 184 of the 271 without missing data. The average seroprevalence was 12.5% (95% confidence interval 9.6-15.4%). With 1,947 person-months of observation obtained from 240 participants who were uninfected at baseline and seen at least twice during the course of the study, the cumulative incidence of HIV seroconversion between November 1990 and December 1991 was 9.4% (95% confidence interval 5.4-13.4%), and the average incidence rate of HIV seroconversion was 9.2 per 100 person-years (95% confidence interval 4.6-13.9 per 100 person-years). In the multivariate analysis, later date of enrollment into the study, having < 3 months experience as a CSW, and use of injectable contraceptives were the only risk factors that remained significant, with relative risks of 2.1 (95% confidence interval 1.2-3.7) for enrollment 3 months later, 3.8 (95% confidence interval 1.0-14.4) for < 3 months experience as a CSW versus > 3 months experience, and 3.9 (95% confidence interval 1.3-11.8) [corrected] for use of injectable contraceptives. In multivariate analysis of the cross-sectional data with 184 participants, of whom 21 were HIV seropositive, risk of HIV seropositivity increased significantly with current syphilis infection (odds ratio 5.8, 95% confidence interval 1.1-31.0). The results of this study will contribute to a better understanding of the risk factors of infection with HIV and thus allow for better targeting of group-specific interventions, particularly for CSWs and their clients. Further investigation of a possible association between injectable contraceptive use and HIV infection is needed.

Frequency and risk of HIV infection among men attending a clinic for STD in Chiang Mai, Thailand.

A prospective study was conducted in the Chiang Mai Sexually Transmitted Diseases Clinic to determine the frequency of HIV seroconversion among men following high risk sexual contacts and to establish risk factors for HIV infection. HIV antibodies were detected in 26 out of 150 men on the initial recruitment with a seroprevalence rate of 21%. Among 124 initial HIV negative subjects; 100, 77, 68, and 55 subjects were followed for 2, 4, 12, and 24 weeks, respectively. One subject had HIV seroconversion documented with the rate of 1.0% (1/100, 95% confidence interval [CI] = 0.03-5.4%). Logistic regression analysis found significantly independent associations of HIV prevalence with prostitute visits at least once a month (OR = 3.6, 95% CI = 1.2-10.9), and with cigarette smoking (OR = 3.5, 95% CI = 1.2-10.5). Intensive health education should be elucidated to decrease the high rate of HIV infection among this population.

Risk factors of HIV-1 infection among female prostitutes in Khon Kaen, Northeast Thailand.

HIV infection has increased to epidemic proportions in Thailand since 1987. There have been separate epidemics among population groups at high risk of infection and significant increases in different localities. The northeast region of Thailand has been affected by the epidemic since early 1989. The purpose of this study was to identify factors associated with HIV transmission among prostitutes during an early phase of the epidemic in the regional center of Khon Kaen. Three hundred and fifty-six prostitutes known to work in the urban area of Khon Kaen (Ampur Muang) in November 1990 were included in the study. Prostitutes were divided into two groups according to the type of place where they worked: direct prostitutes (in brothels, n = 217) and indirect prostitutes (in massage parlors, n = 139). The prevalence of HIV infection was found to be 12% among direct prostitutes and 2% among indirect prostitutes. Four variables were significantly associated with HIV infection after adjusting for confounders by logistic regression analysis: previous work in an area of high HIV prevalence, working in Khon Kaen less than one month, a low price charged for sex and using injectable contraceptives. Follow-up investigations are currently being carried out to explore in detail the association between the use of injectable contraceptives and HIV infection.

PIP: HIV infection has increased to epidemic proportions in Thailand since 1987. There have been separate epidemics among population groups at high risk of infection and significant increases in different localities. The northeast region of Thailand has been affected by the epidemic since early 1989. The purpose of this study was to identify factors associated with HIV transmission among prostitutes during an early phase of the epidemic in the regional center of Khon Kaen. 356 prostitutes known to work in the urban area of Khon Kaen (Ampur Muang) in November 1990 were included in the study. Prostitutes were divided into two groups according to the type of place where they worked: direct prostitutes (in brothels, n = 217) and indirect prostitutes (in massage parlors, n = 139). The prevalence of HIV infection was found to be 12% among direct prostitutes and 2% among indirect prostitutes. Four variables were significantly associated with HIV infection after adjusting for confounders by logistic regression analysis: previous work in an area of high HIV prevalence; working in Khon Kaen less than one month; a low price charged for sex; and using injectable contraceptives. Follow-up investigations are currently being carried out to explore in detail the association between the use of injectable contraceptives and HIV infection. (author's)

Risk factors for HIV among prostitutes in Chiangmai, Thailand.

The discovery of a 44% (44 out of 100) prevalence rate of HIV infection among female prostitutes working in brothels in Chiangmai in Thailand in June 1989, prompted this follow-up study in August to confirm the high prevalence rate and to look for risk factors for infection. We studied 238 female prostitutes working in 14 brothels and confirmed this high prevalence rate. Eighty-seven (36.5%) out of 238 prostitutes were found to be HIV-positive by enzyme-linked immunosorbent assay with IFA or Western blot confirmation. Logistic regressions found a significant association between HIV infection and frequency of sexual intercourse greater than 3 times per day [odds ratio (OR) = 2.82, 95% confidence interval (CI) = 1.47-5.41], sexual service charge less than 150 Baht (OR = 9.1, 95% CI = 2.9-33.3), and post sexual cleansing with water alone (OR = 3.85, 95% CI = 1.90-7.80). Of 56 women found seronegative in the June survey, 35 were re-tested in the August study. Seven (20%) of them were seropositive, giving an HIV seroconversion incidence rate of 10% per month. The findings of this study prompted intensive health education programmes among prostitutes, their customers, and owners of brothels.