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Laboratory Practices for Prenatal Group B Streptococcal Screening and Reporting -- Connecticut, Georgia, and Minnesota, 1997-1998

Group B Streptococcus (GBS) is a leading cause of neonatal sepsis in the United States (1). CDC, in collaboration with the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics, recommends that laboratories adopt optimal screening practices* to identify GBS and to promptly report test results so that GBS-colonized pregnant women can receive antibiotics during labor (1-7). To assess GBS screening practices in clinical laboratories, state health departments surveyed laboratories in Connecticut, Georgia, and Minnesota, participants in the Emerging Infections Program. The survey found that the practices of some participating laboratories were suboptimal, particularly in their lack of use of selective broth media for culture of GBS.

During May 1997-February 1998, surveys were mailed to all microbiology laboratories in Connecticut (46) and Minnesota (153), and to all 59 laboratories in the 20-county metropolitan area of Atlanta, Georgia. The survey asked about the anatomical source of specimens, media used for culture, and methods of reporting GBS test results to health-care providers. Responses to the survey were received from 46 (100%) laboratories in Connecticut, 148 (97%) in Minnesota, and 52 (88%) in Georgia. Responses were analyzed from laboratories that processed GBS specimens (39 [85%] in Connecticut, 38 [73%] in Georgia, and 101 [68%] in Minnesota).

Selective broth media were used in 24 (62%) laboratories in Connecticut, 15 (39%) in Georgia, and 42 (42%) in Minnesota (Table 1). Some laboratories (4%-14% in each state) used antigen detection kits for detecting GBS directly from clinical specimens without culture back-up. Providers were notified when an inappropriate (other than vaginal/rectal) specimen was received in 20 (51%) laboratories in Connecticut and one (3%) in Georgia. In Minnesota, 17 (17%) laboratories informed providers that the specimen was inappropriate when a cervical specimen was submitted. In Connecticut, if specimens were not labeled for a GBS screen, 18 (51%) laboratories processed the specimens without specific steps for GBS identification, 13 (37%) processed specifically for GBS, and four (11%) processed specimens based on anatomical site. In 1998 in Georgia, 19 (58%) of 33 laboratories did not process for GBS when they received genital specimens without specific labeling for GBS. Laboratories used a variety of methods to report test results to health-care providers (Table 1).

During March-May 1998, each of the three state health departments provided the participating laboratories with survey results and recommendations designed to optimize identification of pregnant women colonized with GBS. Follow-up data indicated that in Connecticut, the use of selective broth media increased from 62% to 92%; in Georgia, it increased from 39% to 67%. Minnesota data were not available for this report.

Reported by: A Roome, PhD, H Linardos, J Hadler, MD, State Epidemiologist, Emerging Infections Program, Connecticut Dept of Public Health. R Lynfield, MD, J Besser, MS, S Johnson, K White, MPH, R Danila, PhD, Acting State Epidemiologist, Emerging Infections Program, Minnesota Dept of Health. J Koehler, DVM, A Fiore, MD, P Blake, MD, Acting State Epidemiologist, Epidemiology Section; M Ray, MS, M Park, PhD, Div of Public Health Laboratory, Emerging Infections Program, Div of Public Health, Georgia Dept of Human Resources. W Baughman, MPH, Veterans Administration Medical Center, Emory Univ School of Medicine, Atlanta, Georgia. Respiratory Diseases Br, Div of Bacterial and Mycotic Diseases, and Emerging Infections Program, National Center for Infectious Diseases; and an EIS Officer, CDC.

Editorial Note:

To prevent perinatal GBS disease, screening relies on cultures of vaginal/rectal swabs collected from women at 35 to 37 weeks' gestation followed by intrapartum antimicrobial prophylaxis if the culture is positive (1). When optimally executed, screening can decrease early-onset neonatal GBS disease by 78% (8). Geographic areas with a higher proportion of hospitals with neonatal GBS prevention policies have lower incidence rates of early-onset GBS disease than areas with fewer hospitals with these policies (9). However, screening requires appropriate and accurate specimen collection, labeling, and use of culture media, and effective reporting of results to the health-care providers present at the time of delivery.

Laboratories have a role to play at each step of the GBS screening process. First, specimens should be combined vaginal/rectal swabs. Because vaginal/rectal swabs improve GBS isolation rates by 40% over vaginal specimens alone (2,3), and cervical cultures yield 40% fewer positive cultures than do single vaginal swabs (4), laboratories that receive cervical or vaginal specimens should alert providers that vaginal/rectal specimens are recommended for GBS detection. Second, specimens must be clearly and correctly labeled to avoid inappropriate and potentially costly mistakes in culture methods. Third, laboratories must use an appropriate culture technique. Use of selective broth media can increase GBS isolation by 50% over nonselective media (5-7); of the laboratories surveyed, 38%-61% were not using selective broth media, and 4%-14% continued to use an antigen testing method without culture back-up even though this method has poor sensitivity (10). However, follow-up data from Connecticut and Georgia showed the feasibility for laboratories to switch to selective broth use. Fourth, culture results must be available to labor and delivery providers. From 40% to 79% of laboratories use electronic methods to report GBS test results to providers. Computerized methods of communicating culture results allow continuous, convenient access by multiple providers for individual patients.

The findings in this report are subject to at least two limitations. First, because the survey included only three states, the results might not be applicable to other states. Second, although the respondents provided direct information about laboratory practices, the survey could provide only indirect information on physician practices. Connecticut and Minnesota health departments are conducting studies of health-care provider GBS prevention practices.

Appropriate laboratory practices and cooperation among health-care providers, laboratories, and labor and delivery facilities are integral to effective perinatal GBS disease prevention. An example of a report sent to laboratories in this survey and results and recommendations are available on the World-Wide Web at** and from CDC. Copies of GBS prevention guidelines and other information for health-care providers and pregnant women are available at or from CDC's Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Mailstop C-23, 1600 Clifton Road, N.E., Atlanta, GA 30333.


  1. CDC. Prevention of perinatal group B streptococcal disease: a public health perspective. MMWR 1996;45(no. RR-7).
  2. Badri MS, Zawaneh S, Cruz AC, et al. Rectal colonization with group B Streptococcus: relation to vaginal colonization of pregnant women. JID 1977;135:308-12.
  3. Philipson EH, Palermino DA, Robinson A. Enhanced antenatal detection of group B Streptococcus colonization. Obstet Gynecol 1995;85:437-9.
  4. Regan JA, Klebanoff MA, Nugent RP, et al. The epidemiology of group B streptococcal colonization in pregnancy. Obstet Gynecol 1991;77:604-9.
  5. Altaie SS, Dryja D. Detection of group B Streptococcus: comparison of solid and liquid culture media with and without selective antibiotics. Diagn Microbiol Infect Dis 1994;18:141-4.
  6. Baker CJ, Clark DJ, Barrett FF. Selective broth medium for isolation of group B streptococci. Appl Microbiol 1973;26:884-5.
  7. Baker CJ, Goroff DK, Alpert S, et al. Vaginal colonization with group B Streptococcus: a study in college women. JID 1977;135:392-7.
  8. Rosenstein NE, Schuchat A, Neonatal Group B Streptococcal Disease Study Group. Opportunities for prevention of perinatal group B streptococcal disease: a multistate surveillance analysis. Obstet Gynecol 1997;90:901-6.
  9. CDC. Adoption of hospital policies for prevention of perinatal group B streptococcal disease--United States, 1997. MMWR 1998;47:665-70.
  10. Nightingale SL. Safety alert re risk of misdiagnosis of group B streptococcal infection. JAMA 1997;277:1343.

* Optimal detection of GBS depends on culture of combined vaginal/rectal swabs collected from women at 35 to 37 weeks' gestation and the use of selective broth media (Todd-Hewitt broth with either colistin and nalidixic acid or gentamicin and nalidixic acid). Prenatal screening is one of two strategies recommended for perinatal GBS disease prevention; the alternative is risk-based and identifies candidates for intrapartum antimicrobial prophylaxis based on risk factors present during labor (i.e., gestation at less than 37 weeks, duration of rupture of membranes greater than or equal to 18 hours, and maternal fever) (1).

** References to sites of nonfederal organizations on the World-Wide Web are provided solely as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites.

Table 1

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TABLE 1. Microbiology laboratory practices for group B streptococcal specimen
processing and feedback -- Connecticut, Georgia, and Minnesota, 1997-1998
                              Connecticut (n=39)  Georgia (n=38*)   Minnesota (n=101)
                              ------------------  ---------------   -----------------
Practice                         No.      (%)      No.    (%)          No.   (%)
Receive combined
 vaginal/rectal specimens         27      (69)     18     (47)        55     (54)
Use selective broth media         24      (62)     15     (39)        42     (42)
Use antigen kits without
 culture backup                    4      (10)      5     (14)         4     ( 4)
Method of reporting
 laboratory results to the
  Electronic                      29      (74)     30     (79)        40     (40)
  Courier                         26      (67)     13     (34)        57     (56)
  Telephone                       23      (59)     21     (55)        45     (45)
  Fax                             23      (59)     19     (50)        36     (36)
  Mail                            10      (26)      8     (21)         7     ( 7)
  Other                            2      ( 5)      4     (11)        26     (26)
* Denominator varied because of missing responses.
+ More than one method could be used.

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