Guide to Clinical Preventive Services, 2007

Infectious Diseases

Screening for Asymptomatic Bacteriuria

Summary of Recommendations The U.S. Preventive Services Task Force (USPSTF) strongly recommends that all pregnant women be screened for asymptomatic bacteriuria using urine culture at 12-16 weeks' gestation. Rating: A Recommendation. The USPSTF recommends against the routine screening of men and nonpregnant women for asymptomatic bacteriuria. Rating: D Recommendation.

This USPSTF recommendation was first published by: Agency for Healthcare Research and Quality, Rockville, MD. February 2004.  http://www.ahrq.gov/clinic/3rduspstf/asymbac/asymbacrs.htm.

Clinical Considerations

• The screening tests used commonly in the primary care setting (dipstick analysis and direct microscopy) have poor positive and negative predictive value for detecting bacteriuria in asymptomatic persons. Urine culture is the gold standard for detecting asymptomatic bacteriuria but is expensive for routine screening in populations with a low prevalence of this condition. Results from one study done with a new enzymatic urine screening test (Uriscreen™) showed that the test has a sensitivity of 100 percent and a specificity of 81 percent.
• Good evidence exists that screening pregnant women for asymptomatic bacteriuria with urine culture (rather than urinalysis) significantly reduces symptomatic urinary tract infections, low birth weight, and preterm delivery. A specimen obtained at 12-16 weeks' gestation will detect approximately 80 percent of patients with asymptomatic bacteriuria. The optimal frequency of subsequent urine testing during pregnancy is uncertain.
• Good evidence exists that screening individuals other than pregnant women for asymptomatic bacteriuria does not significantly improve clinical outcomes. Results from a study of women with diabetes who were treated for asymptomatic bacteriuria demonstrated no reduction in complications.¹⁹ Although there were short-term results in clearing bacteriuria with antimicrobial therapy, there was no decrease in the number of symptomatic episodes or hospitalizations over the long term. Furthermore, the high rate of recurrence of bacteriuria in those who were screened and treated resulted in a marked increase in the use of antimicrobial agents.

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Screening for Chlamydial Infection

Summary of Recommendations The U.S. Preventive Services Task Force (USPSTF) strongly recommends that clinicians routinely screen all sexually active women aged 25 years and younger, and other asymptomatic women at increased risk for infection, for chlamydial infection (see Clinical Considerations for discussion of risk factors). Rating: A Recommendation. The USPSTF makes no recommendation for or against routinely screening asymptomatic low-risk women in the general population for chlamydial infection. Rating: C Recommendation. The USPSTF recommends that clinicians routinely screen all asymptomatic pregnant women aged 25 years and younger and others at increased risk for chlamydial infection (see Clinical Considerations for discussion of risk factors in pregnancy). Rating: B Recommendation. The USPSTF makes no recommendation for or against routine screening of asymptomatic, low-risk pregnant women aged 26 years and older for chlamydial infection. Rating: C Recommendation. The USPSTF concludes that the evidence is insufficient to recommend for or against routinely screening asymptomatic men for chlamydial infection. Rating: I Recommendation.

This USPSTF recommendation was first published in:& Am J Prev Med 2001;20(3S):90-4. http://www.ahrq.gov/clinic/ajpmsuppl/chlarr.htm.

Clinical Considerations

• Women and adolescents through age 20 years are at highest risk for chlamydial infection, but most reported data indicate that infection is prevalent among women aged 20-25.
• Age is the most important risk marker. Other patient characteristics associated with a higher prevalence of infection include being unmarried, African-American race, having a prior history of sexually transmitted disease (STD), having new or multiple sexual partners, having cervical ectopy, and using barrier contraceptives inconsistently. Individual risk depends on the number of risk markers and local prevalence of the disease. Specific risk-based screening protocols need to be tested at the local level.
• Clinicians should consider the characteristics of the communities they serve in determining appropriate screening strategies for their patient population.
• More targeted screening may be indicated in specific settings as better prevalence data become available. Prevalence of chlamydial infection varies widely among communities and patient populations. Knowledge of the patient population is the best guide to developing a screening strategy. Local public health authorities can be a source of valuable information.
• The optimal interval for screening is uncertain. For women with a previous negative screening test, the interval for rescreening should take into account changes in sexual partners. If there is evidence that a woman is at low risk for infection (e.g., in a mutually monogamous relationship with a previous history of negative screening tests for chlamydial infection), it may not be necessary to screen frequently. Rescreening at 6 to 12 months may be appropriate for previously infected women because of high rates of reinfection.
• The optimal timing of screening in pregnancy is also uncertain. Screening early in pregnancy provides greater opportunities to improve pregnancy outcomes, including low birth weight and premature delivery; however, screening in the third trimester may be more effective at preventing transmission of chlamydial infection to the infant during birth. The incremental benefit of repeated screening is unknown.
• Screening high-risk young men is a clinical option. Until the advent of urine-based screening tests, routine screening of men was rarely performed. As a result, very little evidence regarding the efficacy of screening in men in reducing infection among women exists. Trials are underway to assess the effectiveness of screening asymptomatic men.
• The choice of specific screening technique is left to clinical judgment. Choice of test will depend on issues of cost, convenience, and feasibility, which may vary in different settings. Although specificity is high with most approved tests, false-positive results can occur with all non-culture tests and rarely with culture tests. Subsequent to initial release of this recommendation, the Centers for Disease Control and Prevention (CDC) released laboratory guidelines that outline the advantages and disadvantages of available tests. These guidelines are available at www.cdc.gov/STD/LabGuidelines.
• Partners of infected individuals should be tested and treated if infected or treated presumptively.
• Clinicians should remain alert for findings suggestive of chlamydial infection during pelvic examination of asymptomatic women (e.g., discharge, cervical erythema, and cervical friability).
• Clinicians should be sensitive to the potential effect of diagnosing a sexually transmitted disease on a couple. To prevent false-positive results, confirmatory testing may be appropriate in settings with low population prevalence.

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Screening for Genital Herpes

Summary of Recommendations The U.S. Preventive Services Task Force (USPSTF) recommends against routine serological screening for herpes simplex virus (HSV) in asymptomatic pregnant women at any time during pregnancy to prevent neonatal HSV infection. Rating: D Recommendation. The USPSTF recommends against routine serological screening for HSV in asymptomatic adolescents and adults. Rating: D Recommendation.

This USPSTF recommendation was first published by: Agency for Healthcare Research and Quality. Rockville, MD, March 2005. http://www.ahrq.gov/clinic/uspstf05/herpes/herpesrs.htm.

Clinical Considerations

• Serological screening tests for genital herpes can detect prior infection with HSV in asymptomatic persons, and new type-specific serological tests can differentiate between HSV-1 and HSV-2 exposure (these tests cannot differentiate between oral vs genital herpes exposure); however, given the natural history of genital herpes, there is limited evidence to guide clinical intervention in those asymptomatic persons who have positive serological test results. False-positive test results may lead to labeling and psychological stress without any potential benefit to patients. Negative test results (both false-negative and true-negative results) may provide false reassurance to continue high-risk sexual behaviors.
• There is new, good-quality evidence demonstrating that systemic antiviral therapy effectively reduces viral shedding and recurrences of genital herpes in adolescents and adults with a history of recurrent genital herpes. There are multiple efficacious regimens that may be used to prevent the recurrence of clinical genital herpes.
• The USPSTF did not examine the evidence for the effectiveness of counseling to avoid high-risk sexual behavior in persons with a history of genital herpes to prevent transmission to discordant partners, or for the primary prevention of genital herpes in persons not infected with HSV. There are known health benefits of avoiding high-risk sexual behavior, including prevention of sexually transmitted infections (STIs) and HIV infection.
• Primary HSV infection during pregnancy presents the greatest risk for transmitting infection to the newborn. The fact that women with primary HSV infection are initially seronegative limits the usefulness of screening with antibody tests. The USPSTF did not find any studies testing the use of antibody screening to find and treat seronegative pregnant women (i.e., those at risk for primary HSV infection) prophylactically. However, the number of seronegative pregnant women one would need to treat to theoretically avoid one primary infection would be very high, making the potential benefit small. At the same time, the potential harm to many low-risk women and fetuses from the side effects of antiviral therapy may be great.
• There is fair evidence that antiviral therapy in late pregnancy can reduce HSV recurrence and viral shedding at delivery in women with recurrent HSV infection; however, there is currently no evidence that antiviral use in women with a history of HSV leads to reduced neonatal infection. Likewise, there is limited information on the benefits of screening women in labor for signs of active genital HSV lesions, and for the performance of cesarean delivery on those with lesions.

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Screening for Gonorrhea

Summary of Recommendations The U.S. Preventive Services Task Force (USPSTF) recommends that clinicians screen all sexually active women, including those who are pregnant, for gonorrhea infection if they are at increased risk for infection (that is, if they are young or have other individual or population risk factors; go to Clinical Considerations for further discussion of risk factors). Rating: B Recommendation. The USPSTF found insufficient evidence to recommend for or against routine screening for gonorrhea infection in men at increased risk for infection (go to Clinical Considerations for discussion of risk factors). Rating: I Recommendation. The USPSTF recommends against routine screening for gonorrhea infection in men and women who are at low risk for infection (go to Clinical Considerations for discussion of risk factors). Rating: D Recommendation. The USPSTF found insufficient evidence to recommend for or against routine screening for gonorrhea infection in pregnant women who are not at increased risk for infection (go to Clinical Considerations for discussion of risk factors). Rating: I Recommendation. The USPSTF strongly recommends prophylactic ocular topical medication for all newborns against gonococcal ophthalmia neonatorum. Rating: A Recommendation.

This USPSTF recommendation was first published in: Ann Fam Med. 2005;3:263-267. http://www.ahrq.gov/clinic/uspstf05/gonorrhea/gonrs.htm.

Clinical Considerations

• Women and men under the age of 25—including sexually active adolescents—are at highest risk for genital gonorrhea infection. Risk factors for gonorrhea include a history of previous gonorrhea infection, other sexually transmitted infections, new or multiple sexual partners, inconsistent condom use, sex work, and drug use. Risk factors for pregnant women are the same as for non-pregnant women. Prevalence of gonorrhea infection varies widely among communities and patient populations. African Americans and men who have sex with men have a higher prevalence of infection than the general population in many communities and settings.
• Individual risk depends on the local epidemiology of disease. Local public health authorities provide guidance to clinicians to help identify populations who are at increased risk in their communities. In communities with a high prevalence of gonorrhea, broader screening of sexually active young people may be warranted, especially in settings serving individuals who are at increased risk. Additionally, clinicians may want to consider other population-based risk factors, including residence in urban communities and communities with high rates of poverty, when making screening decisions. Low community prevalence of gonorrhea infection may justify more targeted screening.
• Screening is recommended at the first prenatal visit for pregnant women who are in a high risk group for gonorrhea infection. For pregnant patients who are at continued risk, and for those who acquire a new risk factor, a second screening should be conducted during the third trimester. The optimal interval for screening in the non-pregnant population is not known.
• Vaginal culture remains an accurate screening test when transport conditions are suitable. Newer screening tests, including nucleic acid amplification tests and nucleic acid hybridization tests, have demonstrated improved sensitivity and comparable specificity when compared with cervical culture. Some newer tests can be used with urine and vaginal swabs, which enables screening when a pelvic examination is not performed.
• Appropriate treatment of gonorrhea infection and administration of prophylactic medication to newborns have been outlined by the Centers for Disease Control and Prevention (CDC) (http://www.cdc.gov/std/treatment/4-2002TG.htm#Gonococcal). Genital infection in men and women may be treated with a third generation cephalosporin or fluoroquinolone, and pregnant women may be treated with third generation cephalosporins. Because of emerging fluoroquinolone resistance, the CDC issued new treatment guidelines in 2004 recommending that men who have sex with men and those who acquired an infection in California, Hawaii, or Asia not be treated with fluoroquinolone antibiotics. If clinicians have not concurrently screened for chlamydial infection, the CDC recommends presumptive treatment for chlamydia at the time of treatment for gonorrhea. In order to prevent recurrent transmission, partners of infected individuals should be tested and treated if infected, or treated presumptively.
• Gonorrhea is a nationally reportable condition. More complete reporting of gonorrhea cases to public health authorities will permit more accurate estimations of gonorrhea prevalence. Improved information will allow clinicians to screen for gonorrhea in ways that improve the balance between benefits and harms for their patients.
• Research priorities for gonorrhea screening include greater understanding of the benefits of screening men at increased risk, especially men who have sex with men, and the role of reporting on gonorrhea rates and testing priorities.

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Screening for Hepatitis B Virus Infection

Summary of Recommendation The U.S. Preventive Services Task Force (USPSTF) strongly recommends screening for hepatitis B virus (HBV) infection in pregnant women at their first prenatal visit. Rating: A Recommendation. The USPSTF recommends against routinely screening the general asymptomatic population for chronic hepatitis B virus infection. Rating: D Recommendation.

This USPSTF recommendation was first published by: Agency for Healthcare Research and Quality, Rockville, MD. February 2004.  http://www.ahrq.gov/clinic/3rduspstf/hepbscr/hepbrs.htm..

Clinical Considerations

• Routine hepatitis vaccination has had significant impact in reducing the number of new HBV infections per year, with the greatest decline among children and adolescents. Programs that vaccinate health care workers also reduce the transmission of HBV infection.
• Most people who become infected as adults or older children recover fully from HBV infection and develop protective immunity to the virus.
• The main risk factors for HBV infection in the United States include diagnosis with a sexually transmitted disease, intravenous drug use, sexual contact with multiple partners, male homosexual activity, and household contacts of chronically infected persons. However, screening strategies to identify individuals at high risk have poor predictive value, since 30 percent to 40 percent of infected individuals do not have any easily identifiable risk factors.
• Important predictors of progressive HBV infection include longer duration of infection and the presence of comorbid conditions such as alcohol abuse, HIV, or other chronic liver disease. Individuals with HBV infection identified through screening may benefit from interventions designed to reduce liver injury from other causes, such as counseling to avoid alcohol abuse and immunization against hepatitis A. However, there is limited evidence on the effectiveness of these interventions.

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Screening for Hepatitis C in Adults

Summary of Recommendation The U.S. Preventive Services Task Force (USPSTF) recommends against routine screening for hepatitis C virus (HCV) infection in asymptomatic adults who are not at increased risk (general population) for infection. Rating: D Recommendation. The USPSTF found insufficient evidence to recommend for or against routine screening for HCV infection in adults at high risk for infection. Rating: I Recommendation.

This USPSTF recommendation was first published in:  Ann Intern Med 2004;140(6):462-4. http://www.ahrq.gov/clinic/3rduspstf/hepcscr/hepcrs.htm.

Clinical Considerations

• Established risk factors for HCV infection include current or past intravenous drug use, transfusion before 1990, dialysis, and being a child of an HCV-infected mother. Surrogate markers, such as high-risk sexual behavior (particularly sex with someone infected with HCV) and the use of illegal drugs, such as cocaine or marijuana, have also been associated with increased risk for HCV infection. The proportion of people who received blood or blood product transfusions before 1990 will continue to decline, and HCV infection will be associated mainly with intravenous drug use and, to some extent, unsafe sexual behaviors.
• Initial testing for HCV infection is typically done by enzyme immunoassay (EIA). In a population with a low prevalence of HCV infection (e.g., 2 percent), approximately 59 percent of all positive tests using the third-generation EIA test with 97 percent specificity would be false positive. As a result, confirmatory testing is recommended with the strip recombinant immunoblot assay (third-generation RIBA).
• Important predictors of progressive HCV infection include older age at acquisition; longer duration of infection; and presence of comorbid conditions, such as alcohol misuse, HIV infection, or other chronic liver disease. Asymptomatic individuals with HCV infection identified through screening may benefit from interventions designed to reduce liver injury from other causes, such as counseling to avoid alcohol misuse and immunization against hepatitis A and hepatitis B. However, there is limited evidence of the effectiveness of these interventions.

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Screening for HIV

Summary of Recommendation The U.S. Preventive Services Task Force (USPSTF) strongly recommends that clinicians screen for human immunodeficiency virus (HIV) all adolescents and adults at increased risk for HIV infection. Rating: A Recommendation. The USPSTF makes no recommendation for or against routinely screening for HIV adolescents and adults who are not at increased risk for HIV infection. Rating: C Recommendation. The USPSTF recommends that clinicians screen all pregnant women for HIV. Rating: A Recommendation. This USPSTF recommendation was first published in: Ann Intern Med. 2005;143:32-37. http://www.ahrq.gov/clinic/uspstf05/hiv/hivrs.htm.

Clinical Considerations

• A person is considered at increased risk for HIV infection (and thus should be offered HIV testing) if he or she reports 1 or more individual risk factors or receives health care in a high-prevalence or high-risk clinical setting.
• Individual risk for HIV infection is assessed through a careful patient history. Those at increased risk (as determined by prevalence rates) include: men who have had sex with men after 1975; men and women having unprotected sex with multiple partners; past or present injection drug users; men and women who exchange sex for money or drugs or have sex partners who do; individuals whose past or present sex partners were HIV-infected, bisexual, or injection drug users; persons being treated for sexually transmitted diseases (STDs); and persons with a history of blood transfusion between 1978 and 1985. Persons who request an HIV test despite reporting no individual risk factors may also be considered at increased risk, since this group is likely to include individuals not willing to disclose high risk behaviors.
• There is good evidence of increased yield from routine HIV screening of persons who report no individual risk factors but are seen in high-risk or high-prevalence clinical settings. High-risk settings include STD clinics, correctional facilities, homeless shelters, tuberculosis clinics, clinics serving men who have sex with men, and adolescent health clinics with a high prevalence of STDs. High-prevalence settings are defined by the Centers for Disease Control and Prevention (CDC) as those known to have a 1% or greater prevalence of infection among the patient population being served. Where possible, clinicians should consider the prevalence of HIV infection or the risk characteristics of the population they serve in determining an appropriate screening strategy. Data are currently lacking to guide clinical decisions about the optimal frequency of HIV screening.
• Current evidence supports the benefit of identifying and treating asymptomatic individuals in immunologically advanced stages of HIV disease (CD4 cell counts < 200 cells/mm3) with highly active antiretroviral therapy (HAART). Appropriate prophylaxis and immunization against certain opportunistic infections have also been shown to be effective interventions for these individuals. Use of HAART can be considered for asymptomatic individuals who are in an earlier stage of disease but at high risk for disease progression (CD4 cell count < 350 cells/mm3 or viral load > 100,000 copies/mL), although definitive evidence of a significant benefit of starting HAART at these counts is currently lacking.
• The standard test for diagnosing HIV infection, the repeatedly reactive enzyme immunoassay followed by confirmatory western blot or immunofluorescent assay, is highly accurate (sensitivity and specificity > 99%). Rapid HIV antibody testing is also highly accurate; can be performed in 10 to 30 minutes; and, when offered at the point of care, is useful for screening high risk patients who do not receive regular medical care (e.g., those seen in emergency departments), as well as women with unknown HIV status who present in active labor.
• Early identification of maternal HIV seropositivity allows early antiretroviral treatment to prevent mother-to-child transmission, allows providers to avoid obstetric practices that may increase the risk for transmission, and allows an opportunity to counsel the mother against breastfeeding (also known to increase the risk for transmission). There is evidence that the adoption of "opt-out" strategies to screen pregnant women (who are informed that an HIV test will be conducted as a standard part of prenatal care unless they decline it) has resulted in higher testing rates. However, ethical and legal concerns of not obtaining specific informed consent for an HIV test using the "opt-out" strategy have been raised. While dramatic reductions in HIV transmission to neonates have been noted as a result of early prenatal detection and treatment, the extent to which detection of HIV infection and intervention during pregnancy may improve long-term maternal outcomes is unclear.

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Screening for Syphilis Infection

Summary of Recommendations The U.S. Preventive Services Task Force (USPSTF) strongly recommends that clinicians screen persons at increased risk for syphilis infection. Rating: A Recommendation. The USPSTF strongly recommends that clinicians screen all pregnant women for syphilis infection. Rating: A Recommendation. The USPSTF recommends against routine screening of asymptomatic persons who are not at increased risk for syphilis infection. Rating: D Recommendation.

This USPSTF recommendation was first published in:  Ann Fam Med 2004;2(4):362-5. http://www.ahrq.gov/clinic/3rduspstf/syphilis/syphilrs.htm.

Clinical Considerations

• Populations at increased risk for syphilis infection (as determined by incident rates) include men who have sex with men and engage in high-risk sexual behavior, commercial sex workers, persons who exchange sex for drugs, and those in adult correctional facilities. There is no evidence to support an optimal screening frequency in this population. Clinicians should consider the characteristics of the communities they serve in determining appropriate screening strategies. Prevalence of syphilis infection varies widely among communities and patient populations. For example, the prevalence of syphilis infection differs by region (the prevalence of infection is higher in the southern U.S. and in some metropolitan areas than it is in the U.S. as a whole) and by ethnicity (the prevalence of syphilis infection is higher in Hispanic and African American populations than it is in the white population).
• Persons diagnosed with other sexually transmitted diseases (STDs) (i.e., chlamydia, gonorrhea, genital herpes simplex, human papilloma virus, and HIV) may be more likely than others to engage in high-risk behavior, placing them at increased risk for syphilis; however, there is no evidence that supports the routine screening of individuals diagnosed with other STDs for syphilis infection. Clinicians should use clinical judgment to individualize screening for syphilis infection based on local prevalence and other risk factors (see above).
• Nontreponemal tests commonly used for initial screening are the Venereal Disease Research Laboratory (VDRL) or Rapid Plasma Reagin (RPR), followed by a confirmatory fluorescent treponemal antibody absorbed (FTA-ABS) or T. pallidum particle agglutination (TP-PA). The optimal screening interval in average- and high-risk persons has not been determined.
• All pregnant women should be tested at their first prenatal visit. For women in high-risk groups, repeat serologic testing may be necessary in the third trimester and at delivery. Follow up serologic tests should be obtained to document decline initially after treatment. These followup tests should be performed using the same nontreponemal test initially used to document infections (e.g., VDRL or RPR) to ensure comparability.

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