Herpes simplex virus type-2 (HSV-2) infection, one of the most common sexually transmitted infections worldwide,1 is the main cause of genital ulcers and may increase susceptibility to human immunodeficiency virus.2–4 As most HSV-2 infections are asymptomatic, seroprevalence data provide a better measure of the burden of genital herpetic disease than clinical data.5,6 We analyzed data collected by the International Agency for Research on Cancer (IARC), the National Cancer Institute in Hanoi, and the Hung Vuong Obstetric and Gynecology Hospital in Ho Chi Minh City (HCMC), Vietnam, as part of a multicentric population-based study of sexually transmitted infection prevalence.7
MATERIALS AND METHODS
Study Population and Enrollment
This cross-sectional study recruited married women registered with family planning clinics in an urban area in HCMC (April–October 1997) and a peri-urban district in Hanoi (April–May 1997).8 The HCMC sample was drawn from three communes randomly chosen out of the 15 that constitute HCMC District 10. The Hanoi sample was drawn from four randomly selected communes of the 26 communes in Soc Son.9 In each location (HCMC, Hanoi), 120 women, ages 15 years and older, were randomly selected within each of 11 age groups. Health workers visited each woman at her home to check exclusion criteria (pregnancy, history of hysterectomy or conization, mental impairment), explain study aims, and obtain written informed consent. Overall, 1122 in HCMC (87.7% of 1279 contacted) and 1246 women in Hanoi (94.4% of 1320 contacted) came to the commune health center for a structured interview and gynecological examination, including a 10-mL blood sample and Pap smear. All protocols were approved by the Ministry of Health Board of Vietnam and the Ethical Committee of the IARC, Lyon, France.
Specimen Processing and Laboratory Techniques
Specimens were shipped daily to central laboratories in each study site for processing and storage. Blood samples were centrifuged at 1500 g. The plasma was placed in Nunc tubes and frozen at −20° C for shipment to Lyon for storage. IgG antibodies against HSV-2 were detected from plasma samples, using Focus Diagnostics/MRL type specific HSV-2 ELISA assays in a central laboratory in Seattle, WA. A formal validation study for HSV-2 was conducted in each site by retesting 100 samples with the Western blot, the gold standard test for type-specific HSV serology.8,10 Index values of <0.9 were classified as negative, those >1.1 as positive, and others as equivocal, according to manufacturer’s instructions. HPV DNA testing was performed on cervical exfoliated cells with a general primer-mediated GP5+/6+-PCR, and PCR positivity was assessed by using 2 HPV oligoprobe cocktails to detect 36 individual HPV types.8,11
Crude and age-standardized (2000 world standard population12) HSV-2 seroprevalence and 95% confidence intervals (CIs) were calculated separately for each study area. Age-adjusted (aaPR) and multiply-adjusted prevalence ratios for HSV-2 seropositivity and CIs were calculated by log-binomial regression, with and without controlling for variables significant in the age-adjusted analysis in either HCMC or Hanoi.
After we excluded women without HSV-2 serostatus data (16 HCMC, 76 Hanoi), data from 1106 women from HCMC and 1170 women from Hanoi were analyzed. HCMC women had more schooling and were older at first pregnancy (Table 1). Fewer HCMC women began coitus before age 19 years. Primary methods of contraception were IUDs (ever used by 55.8% of HCMC women and 43.2% of Hanoi women, not shown) and male condoms (46.7% ever used in HCMC, not shown). Most women reported having had only 1 sexual partner (93.6% HCMC, 94.6% Hanoi). HPV DNA was found in 9.0% of HCMC women and 1.7% of Hanoi women.
HSV-2 seropositivity was higher in HCMC (34.4%, 95% CI: 31.7–37.3; age-standardized: 30.8%, 95% CI: 28.1–33.4) than in Hanoi (9.2%, 95% CI: 7.6–10.9; age-standardized: 8.8%, 95% CI: 7.1–10.5) (Table 2). In HCMC, HSV-2 seroprevalence increased monotonically with age, from 15.7% to 51.5% (aaPR 3.3: 2.2–4.8). HSV-2 seropositivity was inversely associated with educational attainment. HSV-2 seroprevalence was higher in divorced women and widows. The corresponding associations in Hanoi were weaker and less consistent.
Menstrual and Reproductive Factors
Among HCMC women, HSV-2 prevalence was inversely associated with age at first intercourse (aaPR 1.4: 1.1–1.7 for age <19 years) and age at first pregnancy (aaPR 1.3: 1.1–1.6 for age <21 years). HSV-2 prevalence was not related to IUD use, but was higher for women who reported current oral contraceptive use (aaPR 1.5: 1.1–2.2). HSV-2 seroprevalence was higher for nulliparous women. Higher crude HSV-2 prevalence among women reporting 5+ pregnancies likely resulted from confounding by age, since the aaPR for parity were not elevated. HSV-2 was slightly higher for HCMC women who reported a spontaneous abortion, though not for those reporting an induced abortion. Again, the corresponding associations for Hanoi were inconsistent or absent.
HSV-2 prevalence was higher among HCMC women reporting more than one lifetime sexual partner, but not among their counterparts from Hanoi. Moreover, most HSV-2 infections (209/381 in HCMC, 77/108 in Hanoi) occurred in women who reported that both they and their husbands had only 1 sex partner ever. In HCMC, HSV-2 prevalence was higher among HPV DNA positive women (aaPR 1.4: 1.2–1.7); in Hanoi, only 1 HPV DNA positive woman was HSV-2 seropositive.
In multiple regression models, the age-related rise in HSV-2 prevalence was still present in HCMC. Multiply- adjusted prevalence ratios for HCMC were slightly higher than the aaPRs for marital status, age at first pregnancy, and HPV DNA positivity, but weaker for having had more than one sex partner (Table 3).
Age-standardized HSV-2 seroprevalence in ever-married women in HCMC (30.8%) was nearly 3.5 times that in Hanoi (8.8%) despite similarly low proportions of women reporting multiple lifetime sexual partners and earlier onset of sexual intercourse in HCMC. Underreporting of sexual partner risk factors is likely for both geographical areas, as most HSV-2 seropositive women reported only 1 lifetime sex partner. The higher HSV-2 seroprevalence in HCMC was likely not due to false positive tests because all specimens were examined in parallel within the same laboratory.
We believe that the marked difference in HSV-2 seroprevalence between the 2 samples is related to socio-cultural, historical, economic, and demographic factors including urbanicity and migration.13–15 The HCMC sample came from an urban district, and only 44% reported having been born in HCMC. The Hanoi sample was peri-urban, with most women born in Hanoi. The prevalence of HSV-2 and other sexually transmitted infections tends to be higher in urban areas,6,16 and the urban-rural ratio in human immunodeficiency virus seroprevalence among Vietnamese women is about 2:1.17 Regional differences are also likely. The HSV-2 prevalence differential parallels the differential in invasive cervical cancer incidence (26.0/100,000/year in HCMC, 6.3/100,000 in Hanoi18,19), for which HSV-2 may be a cofactor with high-risk HPV infection.20 Also, HSV-2 seroprevalence in female sex workers is higher in southern provinces (Dong Thap 32.3%, An Giang 33.3% and Kien Giang 29.9%) than in a northern border area (Lai Chau 5.0%).21 Such regional differences could reflect South Vietnam’s greater mid-20th century wartime exposure to social, economic, and political disruption, internal migration, and US military personnel and contractors.
The age-standardized HSV-2 prevalence in Hanoi (8.8%) was similar to that reported for several other Asian populations: 9.2% in Manila,16 below 7% in Japanese women,22,23 and 11% among family planning clients in Dhaka,24 and below the 18% in Hong Kong25 and 18.7% among females in Indonesia26 reported by others. The 30.8% in HCMC is higher than these but less than the 41% reported for Jordanian female university students and 42.2% among women attending antenatal clinics in Turkey.27
Our cross-sectional findings for HCMC of a positive association between HSV-2 and age, and of greater HSV-2 prevalence for widows and divorced women than for currently married women are consistent with studies in Brazil,16 Columbia,28 Mexico,29 Peru,28 Spain,28 and the Philippines.16 Similarly, the association of HSV-2 with earlier age at first intercourse is consistent with most6,29 but not all26 reports. The association with history of multiple sexual partners has been regularly observed.6,29,30 Higher HSV-2 seroprevalence among users of hormonal contraceptives has been reported for the Philippines16 but not in several other studies.16,28 Similarly, our finding of an association between HSV-2 seroprevalence and cervical HPV infection is consistent with previous studies.29,31
Although the data were collected in 1997, to our knowledge the current study remains the largest population-based study of HSV-2 seroprevalence conducted in Vietnam to date. Nevertheless, the samples of ever-married women in HCMC and Hanoi were not designed to be representative of the larger Vietnamese population, nor to test rural-urban or regional differences. Future studies are needed to provide national and regional seroprevalence estimates and to obtain data on men and never-married women.
In conclusion, we observed a moderately high prevalence of HSV-2 and associations with traditional HSV-2 risk factors in an urban general population sample of ever-married women in HCMC. A similarly-obtained sample of ever-married peri-urban women in Hanoi had relatively low HSV-2 seroprevalence, with few risk factor associations observed. Our findings are similar to those seen for HPV DNA prevalence in the same 2 geographic sites.8
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