HIV infection and risk factors among female sex workers in southern Vietnam.

OBJECTIVES: To determine the extent of HIV infection among female commercial sex workers (CSW), to identify risk factors, and to provide baseline data for developing and targeting prevention measures. SUBJECTS AND METHODS: A total of 968 female CSW were enrolled in a cross-sectional study from August 1995 to October 1996. Information was obtained from confidential face-to-face interview, physical examination, and laboratory testing. RESULTS: A total of 65.5% of female CSW reported inconsistent condom use. Overall seroprevalence was 5.2%. The highest seroprevalence (9.5%) was detected in An Giang province, a border area adjacent to Cambodia. Out of seven HIV isolates in An Giang province, six were characterized as Thai subtype E and one as subtype B. Multiple logistic regression analysis showed an independent significant association between HIV seroprevalence and the following: age < or = 30 years [odds ratio (OR), 5.1; 95% confidence interval (CI), 1.7-15.2]; high frequency of sex (> 20 times per week; OR, 13.5; 95% CI, 3.6-50.2); inconsistent condom use (OR, 2.8; 95% CI, 1.01-8.0; sign of genital ulcers (OR, 18.1; 95% CI, 1.8-182); venereal warts (OR, 9.0; 95% CI, 2.5-33.0); brothels as sex venue (OR, 7.0; 95% CI, 2.0-24.3); and working at the border area (OR, 5.1; 95% CI, 2.4-11.0). Brothels as work-sites were significantly related to inconsistent condom use and the socioeconomic background of clients. Only 0.5% of CSW reported injecting drug use. CONCLUSIONS: Female CSW at brothels who reported inconsistent condom use and ulcerous sexually transmitted disease, particularly in the border area with Cambodia, had greater risk of HIV infection. Brothels were more frequently used as sex venues in the border area and were more likely to be visited by occasional clients who were difficult to access. Drug use among female CSW in this region was rare. The development of prevention measures should be based on these results.

Predictors of visits to commercial sex workers by male attendees at sexually transmitted disease clinics in southern Vietnam.

OBJECTIVES: To determine the HIV/sexually transmitted disease (STD) status of male patients at STD clinics and factors associated with frequent visits to commercial sex workers (CSW) in southern Vietnam. DESIGN: Cross-sectional survey. METHODS: Confidential interviews and physical and laboratory evaluation of 804 male patients at STD clinics in two semi-rural provinces in the Mekong delta. RESULTS: HIV seroprevalence was 0.5%. The prevalence of urethritis syndrome was 19.3%, gonorrhea 10.2% (Gram-stain positive) and syphilis 2% (reactive rapid plasma reagin test). All the men had visited CSW in the past and 58% had their first sexual experience with a CSW; 73% had visited a CSW in the last 3 years. Married men were equally as likely as single men to have casual partners or to have visited a CSW. The men recruited CSW more from the streets (45%) than from brothels (38%). Factors independently associated with visiting a CSW in the last 3 years included being single [odds ratio (OR), 2.2], age under 20 years (OR, 1.9), having first sexual intercourse with a CSW (OR, 2.1), not having a current girlfriend (OR, 2.1), using alcohol before sex (OR, 2.7) and drug use (OR, 1.8). Only 7% of men used condoms consistently; 70% had never used them. Only 37% had used a condom last time they had intercourse with a CSW. CONCLUSIONS: Prevention programs for men in Vietnam, particularly those who are young or single, need to focus on reducing drug and alcohol consumption and improving condom use with CSWs.

A waterborne outbreak of hepatitis E virus transmission in southwestern Vietnam.

A hepatitis outbreak affecting primarily adults occurred in southwestern Vietnam, along the Hau river bordering Cambodia, in June and July 1994. One month after the outbreak, sera and epidemiologic information were collected from 150 subjects: 50 patient cases, 50 matched, healthy community controls, and 50 geographic controls living 50 km upriver. The prevalence of immunoglobulin G (IgG) to hepatitis E virus (HEV) was significantly (P < 0.001) higher (76%) among cases than among the matched (38%) and geographic (38%) control populations. Immunoglobulin M to HEV was detected by enzyme-linked immunosorbent assay and Western blot in 16% of sera collected from patients one month after the outbreak. Hepatitis E virus RNA was detected with the polymerase chain reaction in 6% of sera from patients; RNA was not detected in either control group. These results indicate that HEV was the etiologic agent responsible for the outbreak. Children were under-represented among clinical cases. River water served as the principal source for drinking and bathing among most (96%) of the case and control study populations. Boiling of drinking water was negatively associated (P < 0.05) with IgG anti-HEV seropositivity. Unusually heavy rainfall likely contributed to conditions that favored the outbreak. This is the first recognized outbreak of epidemic HEV transmission in Indo-China.

Prevalence of enteric hepatitis A and E viruses in the Mekong River delta region of Vietnam.

A study of antibody prevalence for hepatitis A virus (HAV) and hepatitis E virus (HEV) was carried out in southwestern Vietnam in an area adjacent to a known focus of epidemic HEV transmission. The purpose of this investigation was first to provide a prevalence measure of hepatitis infections, and second to determine the outbreak potential of HEV as a function of the susceptible population. Blood specimens collected from 646 persons in randomly selected village hamlets were examined by an ELISA for anti-HEV IgG and anti-HAV IgG. The prevalences of anti-HEV IgG and anti-HAV IgG were 9% and 97%, respectively. There was a significant increase (P < 0.01) in age-specific anti-HEV IgG. A notable increase in anti-HAV IgG prevalence (P < 0.0001) occurred between child populations 0-4 (64%) and 5-9 (95%) years of age. No evidence of familial clustering of anti-HEV IgG-positive individuals was detected, and household crowding was not associated with the spread of HEV. Boiling of water was found to be of protective value against HEV transmission. A relatively low prevalence of anti-HEV indicates considerable HEV outbreak potential, against a background of 1) poor, water-related hygiene/sanitation, 2) dependence on a (likely human/animal waste)-contaminated Mekong riverine system, and 3) periodic river flooding.

Control of dengue fever with active surveillance and the use of insecticidal aerosol cans.

An interventional study was conducted in southern Vietnam to evaluate the feasibility and effectiveness of a new approach to control dengue fever. The approach consisted of active surveillance of dengue patients and the use of insecticidal aerosol cans. Febrile patients were tested serologically at local health centers and insecticidal aerosol cans were given to the family and employed in the neighborhood of dengue patients instead of ultra low volume (ULV) fogging with insecticide. The number of dengue IgM antibody positive cases among febrile patients, the number of reported dengue hemorrhagic fever patients and the total cost were compared in the 2 approaches (prompt focal ULV fogging and the use of insecticidal aerosol cans) in 1997. The aerosol cans were employed 5 times (in June, July, August, September and October) in the study area. ULV fogging in the control area was performed 5 times (in March, May, July, August and September). Twenty-two serologically positive cases were found in the study area which was about half that found in the control area (43 cases). A total of 16 dengue hemorrhagic fever patients was reported in the study area and 43 in the control area. Compared with the reported numbers of the previous year, the reduction rate in the number of dengue hemorrhagic fever cases was 71.4% in the study area and 51.7% in the control area. There were statistically significant differences in the morbidity of dengue fever and the reduction rate of dengue hemorrhagic fever. The cost of the insecticidal aerosol cans was US$393 which was lower than the cost of US$553 for ULV fogging. The findings suggest that insecticidal aerosol cans were effective and feasible for dengue fever control.

A review of Hib epidemiology in Asia.

Meningitis due to an invasive Haemophilus influenzae type b (Hib) infection, has been previously perceived to be relatively uncommon in Asia. However, the incidence of disease and its impact may have been underestimated. In addition to a lack of microbiological facilities in some hospitals, difficulties in culturing the organism and the widespread use of antibiotics may have hidden the true incidence of the disease in some countries. Furthermore, the reported disease burden probably underestimates the incidence of Hib pneumonia. The epidemiology of invasive Hib disease for various Asian nations is reviewed in this paper. Hospital-based studies show that Hib is a major cause of bacterial meningitis and/or pneumonia in the Philippines, India, Thailand, Malaysia, Indonesia and Vietnam. Singapore and Hong Kong have a low incidence of infection compared with Western and other Asian nations. This low incidence is not due to a higher level of natural protective antibodies, but may be related to an interaction between environmental and genetic factors. Therefore the widespread belief that Hib infection is unimportant in Asia does not refer to Asia as a whole and possibly to Chinese patients only, and failure to recognize this has serious implications. The inclusion of Hib vaccine in the routine infant immunization schedule in many industrialized nations has significantly reduced the incidence of invasive disease. Recent studies have shown Hib vaccination is also effective in preventing invasive disease in children in developing countries. While population-based data may be required to confirm the need for public-funded infant Hib immunization in Asia, its introduction in countries with a high incidence of Hib meningitis and/or pneumonia has the potential to significantly improve pediatric health and survival.

The efficacy of a Salmonella typhi Vi conjugate vaccine in two-to-five-year-old children.

BACKGROUND: Typhoid fever is common in developing countries. The licensed typhoid vaccines confer only about 70 percent immunity, do not protect young children, and are not used for routine vaccination. A newly devised conjugate of the capsular polysaccharide of Salmonella typhi, Vi, bound to nontoxic recombinant Pseudomonas aeruginosa exotoxin A (rEPA), has enhanced immunogenicity in adults and in children 5 to 14 years old and has elicited a booster response in children 2 to 4 years old. METHODS: In a double-blind, randomized trial, we evaluated the safety, immunogenicity, and efficacy of the Vi-rEPA vaccine in children two to five years old in 16 communes in Dong Thap Province, Vietnam. Each of the 11,091 children received two injections six weeks apart of either Vi-rEPA or a saline placebo. Cases of typhoid, diagnosed by the isolation of S. typhi from blood cultures after 3 or more days of fever (a temperature of 37.5 degrees C or higher), were identified by active surveillance over a period of 27 months. We estimated efficacy by comparing the attack rate of typhoid in the vaccine group with that in the placebo group. RESULTS: S. typhi was isolated from 4 of the 5525 children who were fully vaccinated with Vi-rEPA and from 47 of the 5566 children who received both injections of placebo (efficacy, 91.5 percent; 95 percent confidence interval, 77.1 to 96.6; P<0.001). Among the 771 children who received only one injection, there was 1 case of typhoid in the vaccine group and 8 cases in the placebo group. Cases were distributed evenly among all age groups and throughout the study period. No serious adverse reactions were observed. In all 36 children studied four weeks after the second injection of the vaccine, levels of serum IgG Vi antibodies had increased by a factor of 10 or more. CONCLUSIONS: The Vi-rEPA conjugate typhoid vaccine is safe and immunogenic and has more than 90 percent efficacy in children two to five years old. The antibody responses and the efficacy suggest that this vaccine should be at least as protective in persons who are more than five years old.

Phase 1 and phase 2 studies of Salmonella enterica serovar paratyphi A O-specific polysaccharide-tetanus toxoid conjugates in adults, teenagers, and 2- to 4-year-old children in Vietnam.

Salmonella enterica serovar Paratyphi A O-specific polysaccharide (O-SP) was activated with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) and bound to tetanus toxoid (TT) with adipic acid dihydrazide as a linker (SPA-TT(1)) or directly (SPA-TT(2)). In mice, these two conjugates elicited high levels of immunoglobulin G (IgG) anti-lipopolysaccharide (LPS) in serum with bactericidal activity (E. Konadu, J. Shiloach, D. A. Bryla, J. B. Robbins, and S. C. Szu, Infect. Immun. 64:2709-2715, 1996). The safety and immunogenicity of the two conjugates were then evaluated sequentially in Vietnamese adults, teenagers, and 2- to 4-year-old children. None of the vaccinees experienced significant side effects, and all had preexisting LPS antibodies. At 4 weeks after injection, there were significant increases of the geometric mean IgG and IgM anti-LPS levels in the adults and teenagers: both conjugates elicited a greater than fourfold rise in the IgG anti-LPS level in serum in >/=80% of the volunteers. SPA-TT(2) elicited slightly higher, though not statistically significantly, levels of IgG anti-LPS than did SPA-TT(1) in these age groups. Accordingly, only SPA-TT(2) was evaluated in the 2- to 4-year-old children. On a random basis, one or two injections were administered 6 weeks apart to the children. No significant side effects were observed, and the levels of preexisting anti-LPS in serum were similar in children of all ages. A significant rise in the IgG anti-LPS titer was elicited by the first injection (P = 0.0001); a second injection did not elicit a booster response. Representative sera from all groups had bactericidal activity that could be adsorbed by S. enterica serovar Paratyphi A LPS.

Safety and immunogenicity of Vi conjugate vaccines for typhoid fever in adults, teenagers, and 2- to 4-year-old children in Vietnam.

The capsular polysaccharide of Salmonella typhi, Vi, is an essential virulence factor and a protective vaccine for people older than 5 years. The safety and immunogenicity of two investigational Vi conjugate vaccines were evaluated in adults, 5- to 14-year-old children, and 2- to 4-year-old children in Vietnam. The conjugates were prepared with Pseudomonas aeruginosa recombinant exoprotein A (rEPA) as the carrier, using either N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP; Vi-rEPA(1)) or adipic acid dihydrazide (ADH; Vi-rEPA(2)) as linkers. None of the recipients experienced a temperature of >38.5 degrees C or significant local reactions. One injection of Vi-rEPA(2) into adults elicited a geometric mean (GM) increase in anti-Vi immunoglobulin G (IgG) from 9.62 enzyme-linked immunosorbent assay units/ml (EU) to 465 EU at 6 weeks; this level fell to 119 EU after 26 weeks. In the 5- to 14-year-old children, anti-Vi IgG levels at 6 weeks elicited by Vi-rEPA(2), Vi-rEPA(1), and Vi were 169, 22.8, and 18.9 EU, respectively (P = 0.0001 for Vi-rEPA(1) and Vi with respect to Vi-rEPA(2)). At 26 weeks, the anti-Vi IgG levels for recipients of Vi-rEPA(2), Vi-rEPA(1), and Vi were 30.0, 10.8, and 13.4 EU, respectively (P < 0.001 for Vi-rEPA(1) and Vi with respect to Vi-rEPA(2)); all were higher than the preinjection levels (P = 0. 0001). Vi-rEPA(2) also elicited the highest anti-Vi IgM and IgA levels of the three vaccines. In the 2- to 4-year-old children at 6 weeks following the first injection, Vi-rEPA(2) elicited an anti-Vi IgG level of 69.9 EU compared to 28.9 EU for Vi-rEPA(1) (P = 0.0001). Reinjection increased Vi antibody levels from 69.9 to 95.4 EU for Vi-rEPA(2) and from 28.9 to 83.0 EU for Vi-rEPA(1). At 26 weeks, anti-Vi IgG levels remained higher than those at preinjection (30.6 versus 0.18 for Vi-rEPA(2) and 12.8 versus 0.33 for Vi-rEPA(1); P = 0.0001 for both). Vi vaccine is recommended for individuals of 5 years of age or older. In the present study, the GM level of anti-Vi IgG elicited by two injections of Vi-rEPA(2) in the 2- to 4-year-old children was higher than that elicited by Vi in the 5- to 14-year-old children (30.6 versus 13.4; P = 0.0001). The safety and immunogenicity of the Vi-rEPA(2) conjugate warrant further investigation.