Chlamydia trachomatis infections are the most commonly reported notifiable
disease in the United States. They are among the most prevalent of all
STDs and, since 1994, have comprised the largest proportion of all STDs
reported to CDC (Table 1). In women, chlamydia infections, which are
usually asymptomatic, may result in pelvic inflammatory disease (PID),
which is a major cause of infertility, ectopic pregnancy, and chronic
pelvic pain. Data from a randomized controlled trial of chlamydia screening
in a managed care setting suggest that such screening programs can lead
to a reduction in the incidence of PID by as much as 60%.1As
with other inflammatory STDs, chlamydia infection can facilitate the
transmission of HIV infection. In addition, pregnant women infected with
chlamydia can pass the infection to their infants during delivery, potentially
resulting in neonatal ophthalmia and pneumonia.
The increase in reported chlamydia infections during the last 10 years
reflects the expansion of chlamydia screening activities, use of increasingly
sensitive diagnostic tests, an increased emphasis on case reporting from
providers and laboratories, and improvements in the information systems
for reporting. However, many women who are at risk are still not being
tested, reflecting, in part, lack of awareness among some health care
providers and the limited resources available to support screening. Chlamydia
screening and reporting are likely to expand further in response to the
recently implemented Health Plan Employer Data and Information Set (HEDIS)
measure for chlamydia screening of sexually active women 15 through 25
years of age who receive medical care through managed care organizations.2To
better monitor trends in disease burden in defined populations during
the expansion of chlamydia screening activities, data on chlamydia positivity
among persons screened in a variety of settings are used; in most instances,
test positivity serves as a reasonable approximation of prevalence.3
In 2000, for the first time, all 50 states and the District of Columbia
had regulations requiring the reporting of chlamydia cases to CDC (Figure
1).
In 2003, 877,478 chlamydia infections were reported to CDC from 50
states and the District of Columbia (Table
1). This case count corresponds
to a rate of 304.3 cases per 100,000 population, an increase of 5.1%
compared with the rate of 289.4 in 2002. The reported number of chlamydia
infections was more than two and one half times the number of reported
cases of gonorrhea (335,104 gonorrhea cases were reported in 2003)
(Table 1).
From 1987 through 2003, the rates of reported chlamydia infection
increased from 50.8 to 304.3 cases per 100,000 population (Figure
2,
Table 1). The continuing increase in reported cases likely represents
the further expansion of screening for this infection, the development
and use of more sensitive screening tests, and more complete national
reporting.
For the years 1999-2001, the chlamydia rates in the Southern region
of the United States were higher than the rates in any other region
of the country (Figures 3-5, Table
3). Before 1996, chlamydia rates
were highest in the West and Midwest, where substantial public resources
had been committed for screening programs in family planning clinics.
For the years 2002-2003, overall rates were highest in the Midwest
although rates among women remained highest in the South. Rates have
remained lowest in the Northeast.
In 2003, the overall rate of reported chlamydia infection among women
in the United States (466.9 cases per 100,000 females) was over 3 times
higher than the rate among men (134.3 cases per 100,000 males), likely
reflecting a greater number of women screened for this infection (Figure
6, Tables 4 and 5). The lower rates among men suggest that many of
the sex partners of women with chlamydia are not diagnosed or reported.
However, with the advent of highly sensitive nucleic acid amplification
tests that can be performed on urine, symptomatic and asymptomatic
men are increasingly being diagnosed with chlamydia infection. From
1999 through 2003, the chlamydia infection rate in males increased
by 46.6% (from 91.6 to 134.3 cases per 100,000 males) compared with
a 18.2% increase in women over this period (from 395.1 to 466.9 cases
per 100,000 females) (Tables 4 and 5).
For women, the highest age-specific rates of reported chlamydia in
2003 were among 15- to 19-year-olds (2,687.3 per 100,000 females) and
20- to 24-year-olds (2,564.4 per 100,000 females). These increased
rates in women may be, in part, due to increased screening in this
group. Age-specific rates among men, while substantially lower than
the rates in women, were highest in the 20- to 24-year-olds (Figure
7, Table 10).
In 2003, the rate of chlamydia among African-American females in
the United States was more than 7 times higher than the rate among
white females (1,633.1 and 217.9 per 100,000, respectively) (Table
11B). The chlamydia rate among African-American males was 11 times
higher than that among white males (584.2 and 52.9 per 100,000 respectively).
Chlamydia screening and prevalence monitoring activities were initiated
in Health and Human Services (HHS) Region X in 1988 as a CDC-supported
demonstration project. From 1988 through 2003, the screening programs
in HHS Region X (Alaska, Idaho, Oregon, Washington) family planning
clinics demonstrated a 52.3% decline in chlamydia positivity from 15.1%
to 7.2% among 15- to 24-year-old women (Figure
9); chlamydia positivity
was adjusted for changes in laboratory test methods and associated
test sensitivity.4,5
In 1993, chlamydia screening services for women were expanded to
three additional HHS regions (III, VII, and VIII) and, in 1995, to
the remaining HHS regions (I, II, IV, V, VI, and IX). In some regions,
federally-funded chlamydia screening supplements local- and state-funded
screening programs.
In 2003, the median state-specific chlamydia test positivity among
15- to 24-year-old women who were screened during visits to selected
family planning clinics in all states and outlying areas was 5.9% (range
2.8% to 18.9%) (Figure 8). In nearly all states chlamydia positivity
was greater than the HP2010 target of 3.0%.6See Appendix (Chlamydia,
Gonorrhea, and Syphilis Prevalence Monitoring) for details.
After adjusting trends in chlamydia positivity to account for changes
in laboratory test methods and associated increases in test sensitivity (see Appendix),
chlamydia test positivity decreased in 4 of 10 HHS
regions from 2002 through 2003, increased in 5 regions, and remained
the same in 1 region (Figure 9). Although chlamydia positivity has
declined in the past year in some regions presumably due to the effectiveness
of screening and treatment of women, continued expansion of screening
programs to populations with higher prevalence of disease may have
contributed to increases in positivity in other regions.
1 Scholes D, Stergachis A, Heidrich
FE, Andrilla H, Holmes KK, Stamm WE. Prevention of pelvic inflammatory
disease by screening
for cervical chlamydial infection. N Engl J Med 1996;34(21): 1362-66.
2 National Committee for Quality
Assurance (NCQA). HEDIS 2000: Technical Specifications, Washington,
DC, 1999, pp. 68-70,
285-286.
3 Dicker LW, Mosure DJ, Levine
WC. Chlamydia positivity versus prevalence: what's the difference?
Sex Transm Dis 1998;25:251-3.
4 Dicker LW, Mosure DJ, Levine
WC, et al. Impact of switching laboratory tests on reported trends
in Chlamydia trachomatis infections. Am J Epidemiol 2000;51:430-5.
5 Centers for Disease Control
and Prevention. Sexually Transmitted Disease Surveillance 2003
Supplement: Chlamydia Prevelance
Monitoring Project Annual Report 2003. Atlanta, GA: U.S. Department of
Health and Human Services (in press).
6 U.S. Department of Health
and Human Services. Healthy People 2010. 2nd ed. With Understanding
and Improving Health and Objectives
for Improving Health. 2 vols. Washington, DC: U.S. Government Printing
Office, November 2000.