Abstract
Sirs: As reported recently by Sundaram et al. 1 herpes simplex virus (HSV) type 1 has replaced HSV-2 as the principal cause of genital herpes in young adults in many developed countries. However, little is known about the trend in developing Asian countries, partly due to a lack of diagnostic virology facilities.
Between 1982 and 2008, 274 cases of suspected genital herpes were sampled from general, primary care and obstetric and gynaecology clinics and wards at the University Malaya Medical Centre, in Kuala Lumpur, Malaysia. HSV was confirmed by immunofluorescence (IF; HSV DFA Typing Kit [Trinity Biotech, Ireland]) or virus isolation in Vero cells. The same laboratory methods were used throughout the study. A total of 118 cases had laboratory confirmation of HSV: between one and six cases annually. Multivariate logistic regression using SPSS 15.0 (SPSS Inc, Chicago, IL, USA) was carried out to determine predictors of genital HSV-1 infection. Variables were selected based on the likelihood ratio test, and those significant at P < 0.05 were included in the final model.
Of the 118 genital herpes cases, 50 (42.4%) were due to HSV-1, while 68 (57.6%) were due to HSV-2. Most cases (78.8%) were female and the mean ages of female and male cases were 30.7 and 40.2 years, respectively. The proportion of genital herpes caused by HSV-1 was 22.5% in the 1980s, but HSV-1 replaced HSV-2 as the predominant cause in the 1990s (53.8%) and 2000s (62.9%) (χ2 = 16.003, P < 0.001), as previously observed. 2 Multivariate analysis confirmed this, with the odds of genital HSV-1 infection increasing by 12.9% every year of HSV isolation (Table 1). The odds of genital HSV-1 are reduced by 5.0% with each additional year of age, confirming that genital HSV-1 is more common in younger adults.1,3 The shift towards genital HSV-1 may be due to reduced childhood acquisition of HSV-1 leading to more susceptible young adults, and changes in sexual behaviour such as an increase in oral sex, which is perceived to be less risky.2,4
Logistic regression analysis of predictors of genital HSV-1 infection
OR = odds ratio; CI = confidence interval; HSV = herpes simplex virus
These predictors were present in the final model
‘Other’ group (n = 3) was not analysed as it is a heterogenous group
Among ethnic groups, HSV-1 was more likely to be isolated from Malay (adjusted odds ratio [OR] = 13.28; 95% confidence interval [CI]: 2.60–67.79) and Indian patients (adjusted OR = 12.44; 95% CI: 2.31–66.95) compared with Chinese. This may be due to cultural differences in sexual behaviour as observed in black and Hispanic populations in the USA 5 but which have yet to be determined in Malaysia.
Although 49 of the 50 genital HSV-1 patients in our study were female patients, this was not a significant predictor in the final model. The small number of male patients is likely to have contributed to this. A predominance of female patients has been reported previously.3,6 Possible reasons for this include higher rates of asymptomatic infection in men, 7 increased susceptibility of the female genital tract to HSV infections 8 and greater awareness by women about sexually transmitted infections.
A previous study from Malaysia showed no differences in age, race and gender among patients with HSV-1 and HSV-2, using univariate analysis and a shorter 10–year study duration. 9 However, in our current study, we used multivariate analysis to adjust for confounding factors, and showed that recent year of isolation, younger age, and Malay and Indian ethnicity were predictors of genital HSV-1 infection. This final model had a satisfactory fit and discrimination (Hosmer and Lemeshow goodness-of-fit test, P = 0.668; receiver operating characteristic curve, area under the curve = 0.858).
In summary, we have also found that HSV-1 has overtaken HSV-2 as the main cause of genital herpes since the 1990s in Malaysia.