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An Evaluation of Surveillance for Chlamydia trachomatis infections in the United States, 1987-1991
Linda A. Webster, Ph.D. Joel R. Greenspan, M.D., M.P.H. Allyn K. Nakashima, M.D. Robert E. Johnson, M.D., M.P.H Division of Sexually Transmitted Diseases and HIV Prevention National Center for Prevention Services
Problem/Condition: Chlamydia is the most common sexually transmitted bacterial pathogen in the United States; however, no precise data on the prevalence and incidence of chlamydia infection are available because currently no comprehensive national surveillance system exists for chlamydia. Despite the absence of such a system, states do report numbers of male and female chlamydia cases to CDC on a quarterly basis.
Reporting Period Covered: This report summarizes and reviews the chlamydia surveillance data received by CDC from 1987 through 1991.
Description of System: Summary data on cases of chlamydia reported to state health departments were sent quarterly to CDC in Atlanta, Georgia. The quarterly data from each state included total number of chlamydia cases by sex and by source of report (public, private).
Results: From 1987 through 1991, the number of states with legislation mandating reporting of chlamydia increased twofold. The reported chlamydia rate from those states also doubled during the same time period, from 91.4 cases per 100,000 population in 1987 to 197.5 cases per 100,000 population in 1991.
Interpretation: This twofold increase in the rate of chlamydia reported to CDC did not represent a doubling in chlamydia prevalence or incidence during this time period. Instead, the increase resulted from the increase in the number of states with reporting laws and from the initial attempts of those states to identify and report diagnosed chlamydia infections.
Actions Taken: More accurate measures of the number of chlamydia infections and of trends in the chlamydia infection rate are needed to justify, develop, and evaluate public health programs to control chlamydia infections. An outline of possible surveillance activities for local communities is presented.
Chlamydia is the most common sexually transmitted bacterial pathogen in the United States (1,2). Chlamydia infections are a major cause of infant pneumonia and neonatal conjunctivitis and of pelvic inflammatory disease and subsequent tubal infertility and ectopic pregnancy in women (3). Although the prevalence of genital chlamydia among women has been reported to range from 8% to 40% (4), no precise data for the prevalence and incidence of chlamydia infection are available because currently no comprehensive national surveillance system exists for chlamydia. A combination of factors has affected our ability to establish a national chlamydia surveillance program and to analyze and interpret chlamydia surveillance data: a) a lack of inexpensive, widely available diagnostic tests for chlamydia, b) a large percentage of asymptomatic infections that can only be detected through active screening programs, c) limited resources to support active screening programs, d) a lack of public health laws in all states requiring that health-care providers and laboratories report cases, and e) a lack of resources in local areas to manage and report information on the large number of chlamydia infections. The absence of a nationwide surveillance system for chlamydia has necessitated the use of nongonococcal urethritis as a surrogate in monitoring trends in chlamydia infections and the use of gonorrhea case counts to estimate the number of chlamydia infections each year (1,5).
Despite the absence of a comprehensive national chlamydia surveillance system, states do report numbers of chlamydia cases among males and females to CDC on a quarterly basis. The following report summarizes and reviews the data received by CDC from 1987 through 1991.
The surveillance case definition for chlamydia involves a laboratory-based diagnosis, namely: a) isolation of C. trachomatis by culture or b) demonstration of C. trachomatis in a clinical specimen by antigen detection methods (6). Summary data on cases of chlamydia reported to state health departments from 1987 through 1991 were sent quarterly to CDC in Atlanta, Georgia. The quarterly data from each state included total number of chlamydia cases by sex and by source of report (public, private). Rates of chlamydia infection were calculated by using estimates of the population for 1987 through 1989 and data from the 1990 census for 1990 and 1991 rates (7,8).
The status of chlamydia reporting legislation was ascertained through a telephone survey of sexually transmitted disease programs in each state. Data were included in this analysis only from those states that had legislation requiring chlamydia reporting, and only for those years in which legislation was effective for the entire 12 months of the year (Table 1). No legislation requiring chlamydia reporting was effective for at least a 1-year period from 1987 through 1991 in the District of Columbia and in the following states: Alabama, Alaska, Arkansas, Colorado, Florida, Louisiana, Maryland, Michigan, Mississippi, New York, Nevada, Pennsylvania, Utah, and West Virginia.
To compute regional rates of chlamydia, we grouped states into the four regions of the United States as defined by the Bureau of the Census: Northeast (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, Rhode Island, Vermont); South (Delaware, Georgia, Kentucky, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia); Midwest (Illinois, Indiana, Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, Wisconsin); and West (Arizona, California, Hawaii, Idaho, Montana, New Mexico, Oregon, Washington, Wyoming).
In 1987, only 18 states had legislation requiring chlamydia reporting (Figure 1). By 1991, the number of states with such legislation had increased to 36. Likewise, the reported chlamydia rate from those states with reporting legislation also increased more than twofold during the same time period, from 91.4 cases per 100,000 population in 1987 to 197.5 cases per 100,000 population in 1991.
In 1991, 28 (78%) of the 36 states with legislation requiring chlamydia reporting reported chlamydia infection rates above the year 2000 objective of 170 cases per 100,000 population (Table 2). The highest reported rates of chlamydia were in the midwestern and western regions of the United States. Specifically, the reported rate of chlamydia was 233.4 cases per 100,000 in the Midwest (117,550 cases), 210.3 in the West (96,791 cases), 177.1 in the South (92,367 cases), and 133.8 in the Northeast (28,011 cases).
Reported chlamydia rates for women far exceeded those for men in the United States during the period 1987 through 1991 (Table 3). Furthermore, although the reported chlamydia rates for men increased only slightly during this time period, the reported rates among women increased 106%. Specifically, the reported rate among women in 1987 was 138.0 cases per 100,000 population, 3.3 times higher than the reported rate among males of 41.9 cases per 100,000 population. By 1991, the reported rate among females was approximately six times higher than the rate reported for males (281.2 cases per 100,000 population vs. 47.7 cases per 100,000 population).
The twofold increase in the rate of chlamydia reported to CDC from 1987 through 1991 did not represent a doubling in chlamydia prevalence or incidence during that time period. Instead, this increase resulted from the increase in the number of states with reporting laws and the initial attempts of those states to identify and report diagnosed chlamydia infections. Likewise, the higher reported rates of chlamydia in the Midwest and the West reflected the substantial resources that were committed to organized screening programs in those regions in the mid- to late 1980s (9,10). The higher reported rates of chlamydia for women from 1987 through 1991 may have reflected the increased detection of asymptomatic infection in women through screening. The lower rates in men suggested that many of the sex partners of women with chlamydia infection were not diagnosed, treated, or reported during this period.
More accurate measures of the number of chlamydia infections and trends in the chlamydia infection rates are needed to justify, develop, and evaluate public health programs to control chlamydia infections. To encourage reporting of chlamydia infections by laboratories and health-care providers, every state should have reporting laws requiring that identified chlamydia infections be reported to appropriate boards of health (11). However, as much as 25% of men and 70% of women with chlamydia infections may be asymptomatic (4). Thus, periodic expanded screening efforts must be initiated to better estimate the prevalence of chlamydia infections in local communities. Such screening efforts should be carried out in a variety of settings, e.g., prenatal clinics, family planning clinics, sexually transmitted disease clinics, adolescent health clinics, correctional facilities and detention centers, hospital emergency departments, student health centers, neighborhood health centers or health maintenance organizations, or drug treatment centers. The prevalence of chlamydia infections in the local communities can then be estimated from the number of persons tested and the number of those persons with positive test results. In addition, these expanded screening efforts could be instrumental in identifying persons with asymptomatic infections who continue to contribute to the transmission of chlamydia infections in a community (10).
To better monitor secular trends in the chlamydia infection rate, ongoing, universal screening should be conducted within a small number of clinic populations (sentinel surveillance sites) in local communities (11). Data should be collected not only on the number of persons tested and the number with positive results in these sentinel sites, but also on the demographic characteristics and selected risk factors of all screened patients. Those data will then allow public health officials to estimate disease frequency, determine secular trends, and focus prevention programs by identifying those at high risk for the disease. Furthermore, monitoring secular trends in these sentinel sites should assist programs in evaluating their chlamydia prevention efforts. For example, decreases in the prevalence of chlamydia infection in these sites could indicate movement from prevalent to incident disease detection or a true decline in the rate of disease transmission due to routine screening, appropriate treatment, or partner notification.
The establishment of better chlamydia surveillance programs in local areas is a crucial first step in being able to more accurately estimate the number of chlamydia infections in the United States each year and to monitor disease trends. Improved chlamydia detection programs, in particular active screening programs in high-risk populations, are even more critical to preventing chlamydia infections and decreasing the $2 billion health-care costs associated with chlamydia infections in the United States annually (12).
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