Questions for Geraldine McQuillan, Ph.D., Infectious Disease Epidemiologist and Lead Author of “Prevalence of Herpes Simplex Virus Type 1 and Type 2 in Persons Aged 14-49: United States, 2015–2016”
Q: In the first bullet in the key findings section of your new report, 47.8% is listed for 2015-2016 herpes simplex type 1 prevalence and 11.9% is listed for type 2. Yet in the last bullet there, it reads that prevalence is 48.1% and 12.1%. Why are these estimates different?
GM: This report offers two statistical estimates – a crude rate, or “real” prevalence estimate, and an age-adjusted one. If you look at the data table for Figure 1, you can see that the unadjusted prevalence — or the true prevalence for herpes simplex virus type 1 (HSV-1) — is 47.8% in the U.S population. In order to compare across subgroups that have differing age distributions, we need to age-adjust the data to allow for a more accurate comparison among groups. The age-adjusted prevalence for the total population is 48.1%. Crude rates are influenced by the underlying age distribution of a population, and age-adjusting the rates assures that differences are not due to the age distribution of the populations being compared.
Q: What made you decide to focus on the prevalence of the herpes simplex virus for the subject of your new report?
GQ: Our main motivation for conducting this study is to offer a current assessment of herpes prevalence in the United States. Though we have included HSV-1 and -2 testing in the National Health and Nutrition Examination Survey (NHANES) since 1999, we have not looked at the data since 2010 (Bradley et al. Seroprevalence of herpes simplex virus type 1 and 2 – United States, 1999-2010. JID 2014:209; 325-333). With the addition of six more years of data and a sufficient amount of years to look at trends over time, we decided it was time to re-look at the prevalence of these common viruses in the United States.
Q: Was there a result in your study that you had not expected and that really surprised you?
GQ: The decline in herpes simplex virus type 2 (HSV-2) across all race and ethnic groups was quite striking. The linear decline in prevalence was seen in the previous study for HSV-1 that used data from 1999-2010. There was no decline with the prevalence of HSV-2 at that time. With the addition of six more years of data, we now also see a linear downward trend for HSV-2 and again for HSV-1. We did not expect to see the decline of HSV-2 in all race and ethnic subgroups.
Q: What differences or similarities did you see among race and ethnic groups, and various demographics, in this analysis?
GQ: The difference by race and ethnic subgroups in herpes simplex virus prevalence did not differ from previous reports even with the declines in prevalence in both viruses. Mexican-Americans still have the highest prevalence of HSV-1, and non-Hispanic whites have the lowest. The prevalence of HSV-2 is highest in the non-Hispanic black population and lowest in the non-Hispanic Asian population. Non-Hispanic whites and Mexican- Americans have a similar prevalence. All these race/ethnic differences have been seen in many of our infectious diseases especially those that are transmitted sexually.
Q: What is the take-home message of this report?
GQ: This is a good news data report. I think its take-home message is that two of our most prevalent viruses, HSV-1 and HSV-2, are steadily declining in the U.S population. Though NHANES provides prevalence estimates (new and old infections), once a person is infected with a herpes virus they are infected for life. The only way we see a decline is if there is a drop in new infections or a decrease in the incidence of both HSV-1 and HSV-2. While this report is a presentation of data findings, and did not go into an analysis of risk factors to determine why we are seeing this decline, other industrialized countries have observed declines in HSV-1 during the past two decades. Improvements in living conditions, better hygiene and less crowding likely explain these declines. Other countries who also have seen a decline in HSV-2 in their populations, suggest that the increase in safe-sex practices in the post-AIDS pandemic may contribute to the decline.