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FDA Safety Alert: Risks of Devices for Direct Detection of Group B Streptococcal Antigen

(You are encouraged to copy and distribute this Alert)

     FDA wants to alert you to potentially fatal misdiagnoses when using test kits to detect group B streptococcal (GBS) antigen, and to provide guidelines on how to appropriately use these tests. GBS disease continues to be a major cause of illness and death among neonates. Antigen tests for GBS have produced false negative results from specimens from pregnant women and infants with subsequent infant deaths from GBS disease. GBS antigen tests have also produced false positive results which may lead to inappropriate antibiotic therapy and prolonged hospitalization.

     It is important that clinicians understand the limitations of these devices. Antigen tests are an adjunct to diagnosis and multiple studies have shown that antigen tests are NOT an appropriate substitute for properly performed bacterial culture in the diagnosis of GBS colonization or infection.^1-4

     In order to minimize the likelihood of misdiagnosing GBS infection, we urge that users adhere to the following guidelines. These guidelines should be distributed to all appropriate clinical laboratory personnel, including laboratories in physicians' offices, and physicians and nurses who may use or request these tests. (We have asked manufacturers to notify their customers of the information in this Alert.)

Use in maternity patients

• GBS antigen tests cannot be relied upon to exclude GBS colonization in a pregnant woman. Negative GBS antigen test results should be confirmed using selective broth culture which is more sensitive than antigen tests.

Use in infants

• The only specimens recommended for testing with these devices are blood, serum or cerebrospinal fluid. Testing infant urine with these devices is not recommended.

• These devices should not be used as a substitute for bacteriologic culture in the diagnosis of GBS septicemia and/or meningitis. A positive result indicates only the presence of GBS antigen, and not necessarily the presence of viable organisms. Positive or negative results should be considered presumptive and confirmed by culture.

     New information on the prevention of GBS disease is described in the recent consensus of the Centers for Disease Control and Prevention (CDC)⁵, the American College of Obstetricians and Gynecologists⁶, and the American Academy of Pediatrics⁷. This consensus resulted in a new standard for detecting GBS colonization in pregnant women. Vaginal/rectal cultures should be obtained at 35-37 weeks of gestation and be performed using selective broth media. The consensus also presented a new algorithm for management of a neonate born to a mother who received intrapartum prophylaxis for prevention of early-onset GBS disease.

     FDA has informed manufacturers of test kits for detecting GBS antigen that these devices must be evaluated according to current CDC recommendations as a condition for remaining on the market.

     The Safe Medical Devices Act of 1990 (SMDA) requires hospitals and other user facilities to report deaths and serious illnesses and injuries associated with the use of medical devices. Thus, under the law, an erroneous result from a GBS antigen test kit that results in a death or serious illness must be reported. We request that you follow the procedures established by your facility for such mandatory reporting.

     Even if a report is not mandatory, it would be helpful to report directly to MedWatch, the FDA's voluntary reporting program. Submit these reports to MedWatch: by telephone at 1-800-FDA-1088, by FAX at 1-800-FDA-0178, or by mail to:

MedWatch
Food and Drug Administration
HF-2
5600 Fishers Lane
Rockville, MD 20857

     If you have any questions with regard to this Safety Alert, please contact Nancy Pressly, Office of Surveillance and Biometrics, HFZ-510, 1350 Piccard Drive, Rockville, MD 20850, FAX 301-594-2968, or e-mail nap@cdrh.fda.gov.

References:

¹ Baker, C.J. Inadequacy of rapid immunoassays for intrapartum detection of group B streptococcal carriers. Obstetrics & Gynecology, 88: 51-55, 1996.

² Greenberg, D. N., D. P. Ascher, B. A. Yoder, D. M. Hensley, H.S. Heiman and J. F. Keith, III. Sensitivity and specificity of rapid diagnostic tests for detection of group B streptococcal antigen in bacteremic neonates. J. Clin. Microbio., 33: 193-198, 1995.

³ Perkins, M.D., S. Mirrett and L. B. Reller. Rapid bacterial antigen detection is not clinically useful. J. Clin. Microbio., 33: 1486-1491, 1995.

⁴ Williamson, M., S. H. Fraser and J. Tilse. Failure of the urinary group B streptococcal antigen test as a screen for neonatal sepsis. Arch. Dis. Childhood, 73: F109-111, 1995.

⁵ Centers for Disease Control and Prevention. Prevention of perinatal group B streptococcal disease: A public health perspective. In Morbidity and Mortality Weekly Report (MMWR), Recommendations and Reports, Vol. 45, RR-7, May 31, 1996. Erratum: MMWR, Vol. 45, No. 31, 1996.

⁶ American College of Obstetricians and Gynecologists. Prevention of early-onset disease in the newborn due to group B streptococcus. ACOG Committee Opinion, No. 173, 1996.

⁷ American Academy of Pediatrics. Revised guidelines for prevention of early-onset group B streptococcal infection. Pediatrics, 99: 489-496, 1997.

Updated April 2, 1997

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