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Susceptibility to Vaccine-Preventable Diseases in a Sexually Transmitted Disease Clinic Population


Original Articles

Background and Objective: Sexually transmitted disease (STD) clinics often serve a population that has low medical care utilization. The objective of this study was to determine the susceptibility of an STD clinic population to vaccine-preventable diseases.

Study Design: A cross-sectional study of immunization practices and susceptibility to vaccine-preventable diseases was undertaken by enrolling consecutive patients attending an STD clinic. Demographic information and a history of disease or immunization was assessed by interview. Immunity to measles and rubella was determined by measuring IgG antibodies by ELISA assays.

Results: Of the 288 patients evaluated, the mean age was 28 years and 70.5% were male. Serologically, 16.3% were susceptible to rubella and 8% to measles. Only 8% reported hepatitis B immunization. Although measles protection was high, nearly one in six was susceptible to rubella. Hepatitis B immunization was severely underused.

Conclusion: Baltimore STD clinic patients may benefit from an enhanced rubella and hepatitis B prevention strategy.

* From the Johns Hopkins University School of Medicine; the †Baltimore City Health Department; the ‡Johns Hopkins University School of Hygiene and Public Health, Department of International Health; and the §Johns Hopkins University School of Medicine, Division of Infectious Diseases; Baltimore, Maryland

The authors thank the clinicians and staff at the Druid District Sexually Transmitted Disease Clinic of the Baltimore City Health Department.

Reprint requests: Dr. Mary Allen Staat, Children's Hospital Medical Center, Division of Infectious Diseases, 3333 Burnet Ave., Cincinnati, OH 45229-3039.

Received for publication December 18, 1997, revised March 25, 1998, and accepted March 30, 1998.

THERE HAS BEEN increasing concern over suboptimal immunization rates, especially in medically underserved populations. Ensuring access to early childhood immunization has been the major focus of the public health response. Adolescents and young adults, however, may be at increased risk for vaccine-preventable diseases either because of suboptimal primary immunization or waning immunity. Surveys of rubella cases and large serosurveys of military recruits suggest that high proportions of young adults may be susceptible to measles and rubella.1–4 During the measles epidemics of the early 1990s, adolescents and young adults were disproportionately affected.5 Adolescents and young adults, especially males, often lack adequate access to health care. Sexually transmitted disease (STD) clinics provide targeted medical care to this population. Many, recognizing access issues, have attempted to expand the spectrum of clinical services. We studied whether patients attending STD clinics have high susceptibility to vaccine-preventable diseases, specifically to measles and rubella, to determine whether STD clinics may provide an appropriate health care access point for immunization.

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In August 1994, consecutive patients attending the Druid STD clinic in West Baltimore were asked to enroll in a cross-sectional study of immunization practices and susceptibility to vaccine-preventable diseases. The clinic serves a predominately African-American population with high rates of STD. After informed consent, subjects were interviewed by one of the authors (Y.-L.T.) for demographic information; a history of measles, rubella, and other vaccine-preventable diseases; and immunization (both adult and childhood). Human immunodeficiency virus (HIV) and STD risk factors were abstracted from the medical record. IgG antibodies to measles and rubella were measured using commercial ELISA assays (Measelisa II and Rubelisa II; BioWhittaker, Walkersville, MD). The measles ELISA assay has a sensitivity of 99.4% and a specificity of 96.7%, and the rubella ELISA assay has a sensitivity and specificity of 98.8% and 100%, respectively. The susceptibility (absence of antibody) to each disease was evaluated overall and stratified by age and sex. Proportions were compared by chi-square statistics using PC SAS 6.04 (SAS Institute, Cary, NC).

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Study Population

Subjects were representative of patients attending the STD clinic. Over 60% had a symptomatic STD or were a sexual contact of a patient with a diagnosed STD. The mean age of the sample population was 28 years (range, 14-67) with 17.0% older than 37 years of age. Most subjects were born in Baltimore (73.6%). Fifty-six percent had children in their household. Only 37.5% had a regular health care source. Nearly one-third (30%) had been incarcerated in the past, whereas 11.5% had served in the military (Table 1).



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Immunization History

Nearly all subjects reported being immunized as a child (99.6%), with 44% receiving immunizations at a public clinic and 38% at a private clinic. Only 23 of 287 (8%) reported hepatitis B immunization, and of these, half were immunized in the military. Few reported receiving second doses of measles (21.7%) or rubella (21.0%) vaccines, whereas nearly two thirds reported receiving tetanus boosters after having a cut or laceration. Although 21.1% reported having a history of measles, less than 1% reported a history of rubella. Only two people in the study reported religious objections to immunization (Table 1).

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Overall, 8% of subjects were susceptible to measles and 16.3% were susceptible to rubella. There was no statistical difference in the proportion of subjects susceptible by sex or source of health care (Table 2). For measles, patients older than 37 years of age showed a trend toward being more protected against measles (P = 0.07) than the younger patients. However, for rubella, no statistically significant difference was seen. Susceptibility was not found to be related to any demographic risk factors, immunization history, or STD/HIV risk factors, including a history of drug use. A history of measles was only 86% specific compared with serology.



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Our study demonstrated high rates of protection against measles in this predominantly poor inner-city population. The susceptibility to measles in our population was less than what was seen in population-based studies conducted 5 years before our study.1–3 In those surveys conducted in 1989 in United States military recruits, susceptibility of measles ranged from 17.8% to 21.3%.1–3 In one of the studies, rates from 1989 and 1990 were compared and a decrease in susceptibility was seen from 21.3% in 1989 to 12.5% in 1990.3 Our findings of high levels of protection were unexpected but may have resulted from mass immunization campaigns in the community, increases in exposure to natural disease during the 1990 to 1991 epidemic, or both. Although measles is at an all time low with only 309 cases in 1995, 44% of cases occurred in those at least 15 years of age.5 In 1990, however, there were 27,786 cases, a fivefold increase from the early 1980s, with 33% occurring in those at least 15 years of age,5 which prompted the American Academy of Pediatrics and the Advisory Committee on Immunization Practices to recommend changing the measles immunization schedule to a two-dose strategy.

The measles-mumps-rubella vaccine is recommended for all persons, including HIV-infected persons without severe immunocompromise who do not have evidence of measles immunity. Therefore, evaluation and testing of asymptomatic persons to determine their HIV status is not necessary.6 The 1990 epidemic highlighted the need to do periodic surveys in the future to ensure levels remain high in nonepidemic years.

Rubella susceptibility remains a problem in adolescent and young-adult inner-city populations. Nearly one in six were found to be susceptible to rubella, and therefore this sexually active population is at high risk for both rubella and its adverse fetal outcomes. The Centers for Disease Control and Prevention (CDC) recommends rubella vaccination to men and women who are susceptible.5 Some STD programs offer contraceptive services to women and routinely perform rubella testing and could include rubella vaccine as part of this program. Given the high proportion of susceptible patients in our study, Baltimore STD clinic patients may benefit from an enhanced rubella prevention strategy. As with any live virus vaccine, the measles-mumps-rubella vaccine or any component of the vaccine should not be given to women known to be pregnant or who are considering becoming pregnant within 3 months of vaccination.5

We found hepatitis B immunization to be severely underused in this high-risk population. In a sexually active population, with many people using intravenous drugs or having partners that use intravenous drugs, hepatitis B immunization should be readily available. The CDC has recommended hepatitis B immunization as STD treatment guidelines since 1989 and recommends the vaccine for adolescents and adults, not previously immunized, who are at increased risk for infection. Increased risk categories include those who have multiple sex partners (at least one partner in a 6-month time period), use illegal injecting drugs, are males who have sex with males, or have sexual or regular household contact with a person who is hepatitis B surface antigen positive.5 Patients seeking care at an STD clinic may be in one of these high-risk groups and would therefore be candidates for the vaccine. Determining whether it would be cost-effective to screen patients for hepatitis B infection before the administration of the vaccine would depend on the seroprevalence of hepatitis B infection in that population, the likelihood of compliance, and the cost of the vaccine.7,8 Although the immunization series may be difficult to complete, demonstration projects in similar populations found that routine hepatitis B vaccination in STD and adolescent clinic populations can be accomplished.8–13 Although optimal immunization includes a series of three immunizations, there is evidence that an incomplete series of two doses of the hepatitis B vaccine may provide protective levels in greater than 83% of recipients.14 Multiple studies in similar high-risk populations demonstrated low usage of the vaccine and missed opportunities for immunization in these populations.15–17 To reach the Healthy People 2000 objective to increase hepatitis B vaccination among high-risk populations to at least 90%,18 creative strategies to reach these populations need to be created.

STD clinics are often a primary point of health care access to uninsured or underinsured adolescents and young adults, especially men, without other serious medical problems. With high susceptibility rates for rubella identified in this STD clinic population, one potential intervention would be to offer vaccinations to all individuals attending the STD clinic settings. In addition, the first dose of hepatitis B vaccine could be provided, after obtaining a blood sample for hepatitis B serology. Upon returning to the clinic, those individuals who are susceptible could be given the subsequent doses. This strategy was shown to be a viable method of immunizing an STD clinic population and demonstrated the feasibility of an STD clinic as a health care setting for adult vaccination programs.11 To optimize immunization of adults, STD clinics may be an appropriate venue for measles, rubella, and hepatitis B immunization programs because they access an underserved, often hard to access, susceptible high-risk population.

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