Putting Prevention into Practice An Evidence-Based Approach

Screening for Chlamydial Infection



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Am Fam Physician. 2008 Dec 15;78(12):1349-1350.

This clinical content conforms to AAFP criteria for evidence-based continuing medical education (EB CME). See CME Quiz on page 1341.

Case Study

A 20-year-old woman comes to your office for her initial prenatal visit following a positive home pregnancy test. Her last menstrual period was 10 weeks ago. She is in a monogamous relationship and uses condoms inconsistently. Her only complaint is morning sickness.

Case Study Questions

  1. Based on the information from the U.S. Preventive Services Task Force (USPSTF), which one of the following statements about chlamydia screening in this patient is correct?

    • A. The USPSTF would not recommend routinely screening this patient for chlamydia if she had no risk factors other than her age.

    • B. The patient should be screened at the initial visit and screened again during the second trimester.

    • C. The benefits of screening pregnant women at increased risk are small.

    • D. All pregnant women should be routinely screened regardless of individual risk factors.

    • E. The risk factors for pregnant women are the same as those for nonpregnant women.

  2. Which one of the following statements about screening for chlamydia is correct?

    • A. You must perform a pelvic examination to screen for chlamydia.

    • B. Nucleic acid amplification tests have low sensitivity and specificity compared with vaginal cultures in identifying chlamydia in asymptomatic women.

    • C. In populations with a low prevalence of chlamydial infection, a positive test is more likely to be a false positive than a true positive, even with the most accurate tests available.

    • D. Women younger than 25 years who are sexually active have a risk of chlamydial infection similar to that of women 25 years and older.

    • E. It is not necessary to test patients at increased risk of other sexually transmitted infections such as gonorrhea.

  3. If the patient's chlamydia screening test is positive, which of the following actions is/are appropriate?

    • A. Treat with a single oral dose of 1 g azithromycin (Zithromax) or with 500 mg amoxicillin orally three times daily for seven days.

    • B. Treat with 100 mg doxycycline (Vibramycin) orally twice daily for seven days.

    • C. Delay treatment until the second trimester.

    • D. Instruct the patient to have her sex partner tested for chlamydia and treated, if infected, or treated presumptively.

Answers

1. The correct answer is E. The USPSTF recommends that all pregnant women 24 years and younger, and older pregnant women who are at increased risk should be screened for chlamydia. The USPSTF recommends against routinely screening for chlamydia in women 25 years and older who are not at increased risk, regardless of pregnancy status.

Risk factors for pregnant women are the same as those for nonpregnant women. These include age, inconsistent use of condoms, new or multiple recent sex partners, a history of chlamydia or other sexually transmitted infections, and exchanging sex for money or drugs.

The USPSTF recommends that pregnant women who are at increased risk of chlamydia be screened at the first prenatal visit. Additional screening during the third trimester is recommended in women who continue to be at increased risk of chlamydia, or in whom new risk factors have been identified (e.g., a new sex partner).

Although studies have not directly addressed the effectiveness of screening for chlamydia in pregnant women, the USPSTF found that there is a high prevalence of infection among pregnant women at increased risk, that screening accurately identifies infection in asymptomatic pregnant women, and that treatment for chlamydia improves pregnancy and birth outcomes. Therefore, the USPSTF concluded that the benefits of screening pregnant women at increased risk are substantial.

2. The correct answer is C. In low-prevalence populations, a positive test is more likely to be a false positive than a true positive, even with the most accurate tests available. When evaluating female patients who are not at increased risk of chlamydia, physicians should consider the characteristics of their communities (see accompanying table). Local public health authorities can be a valuable source of information.

Nucleic acid amplification tests have a high sensitivity and specificity when used to screen for chlamydia and can be performed on urine and vaginal swabs. A pelvic examination is not required for screening, although physicians may choose to perform a pelvic examination for other reasons (e.g., cervical cancer screening).

Women younger than 25 years are more than five times more likely to be infected with chlamydia compared with women older than 30 years. Chlamydia and gonorrhea are the two most commonly reported sexually transmitted bacterial infections in the United States. The USPSTF also recommends routine screening for gonorrhea in sexually active women at increased risk.

Table.

Populations with Higher Prevalence of Chlamydia than the General Population

Blacks

Hispanics

Incarcerated populations

Military recruits

Patients at public sexually transmitted infection clinics

Table.   Populations with Higher Prevalence of Chlamydia than the General Population

View Table

Table.

Populations with Higher Prevalence of Chlamydia than the General Population

Blacks

Hispanics

Incarcerated populations

Military recruits

Patients at public sexually transmitted infection clinics

3. The correct answers are A and D.Guidelines from the Centers for Disease Control and Prevention (CDC) recommend treatment of chlamydial infection in pregnant women with a single oral dose of 1 g azithromycin or with 500 mg oral amoxicillin three times daily for seven days. Because these medications are considered safe to use in pregnancy, it is not appropriate to delay treatment. Doxycycline is a pregnancy category D medication, and therefore is contraindicated in pregnant women. The CDC's Web site (http://www.cdc.gov/std/treatment) contains additional information and updates.

Because of high rates of reinfection, the USPSTF advises that physicians ensure that all sex partners of infected persons are tested and treated as appropriate, or treated presumptively.

SOURCES

Centers for Disease Control and Prevention, Workowski KA, Berman SM. Sexually transmitted diseases treatment guidelines, 2006 [published correction appears in MMWR Recomm Rep. 2006;55(36):997]. MMWR Recomm Rep. 2006;55(RR-11):1–94.

Meyers DS, Halvorson H, Luckhaupt S. Screening for chlamydial infection: an evidence update for the U.S. Preventive Services Task Force. Ann Intern Med. 2007;147(2):135–142.

Meyers DS, Halvorson H, Luckhaupt S. Screening for chlamydial infection: a focused evidence update for the U.S. Preventive Services Task Force. Evidence synthesis no. 48. Rockville, Md.: Agency for Healthcare Research and Quality, 2007. http://www.ahrq.gov/clinic/uspstf07/chlamydia/chlamydiasyn.pdf. Accessed October 17, 2008.

U.S. Preventive Services Task Force. Screening for chlamydial infection: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2007;147(2):128–134.

The case study and answers to the following questions on screening for chlamydial infection are based on the recommendations of the U.S. Preventive Services Task Force (USPSTF), an independent panel of experts in primary care and prevention that systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services. More detailed information on this subject is available in the USPSTF Recommendation Statement, the evidence synthesis, and the evidence update summary on the USPSTF Web site (http://www.ahrq.gov/clinic/uspstfix.htm). The evidence synthesis and Recommendation Statement are available in print through the AHRQ Publications Clearinghouse (800–358–9295, e-mail, ahrqpubs@ahrq.hhs.gov). The practice recommendations in this activity are available at http://www.ahrq.gov/clinic/uspstf/uspschlm.htm.


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