Georgia epidemiology report, Vol. 20, no. 11 (Nov. 2004)

November 2004

volume 20 number 11

Laboratory Practices for Prenatal Group B Streptococcal Screening--Georgia, 2003

Background: Group B Streptococcus (GBS) is the leading cause of serious bacterial infections in U.S. newborns. As one of 11 states participating in the Centers for Disease Control and Prevention (CDC) Emerging Infections Program (EIP), Georgia is trying to identify ways to reduce GBS disease, beginning with recognition of cases. Active surveillance for perinatal GBS disease and efforts to improve disease control have been underway in eight counties of the Atlanta Metropolitan Statistical Area (MSA) since 1989. The area was expanded to the 20-county MSA in 1997, and expanded again to include all 159 counties statewide in January 2004 (Figure 1). Surveillance has shown that rates of early-onset GBS disease (during the first week of life) are higher in Georgia than in all EIP states combined (Figure 2).
Until a GBS vaccine becomes available, prevention of perinatal GBS disease will likely depend on recognition of mothers and infants at risk, and targeted interventions to prevent peripartum transmission and disease. New national guidelines for prevention of early-onset GBS disease were released in August 2002, recommending culture-based screening for maternal GBS colonization late in pregnancy to identify candidates for intrapartum antibiotic prophylaxis (IAP)1. These guidelines followed evidence that this approach is more effective in preventing perinatal GBS than risk-factor identification during labor and delivery1, 2. Implementing and optimizing culture-based screening requires cooperation between prenatal care providers, laboratories, and hospital systems to accurately identify colonized mothers and report results in time for labor. Laboratories are key partners in this system, and have recently been asked to enhance their practices for handling and processing GBS screening cultures and for communicating results.
Methods: In July and August 2003, The Georgia EIP conducted a statewide survey of laboratories to assess practices for processing GBS screening cultures. The

survey addressed methods for GBS isolation, identification, and antibiotic susceptibility testing from prenatal specimens during 2003. It was mailed or administered over the phone to personnel in 99 clinical laboratories throughout Georgia.

Results: Participants in the Survey: Respondents were laboratorians that work in microbiology laboratories and participate in active bacterial surveillance for the

Figure 1. Georgia Emerging Infections Program surveillance areas, MSA* and GOA**, by county.

Per 1000 live births

*MSA: 20-county Atlanta Metropolitan Statistical Area **GOA, Georgia Outside Atlanta: 139-county area surrounding the MSA
Roughly 50% of the state population lives in each of the two surveillance areas
Figure 2. Early onset GBS, rate per 1000 live births, Atlanta MSA vs. EIP
1 0.8 0.6 0.4 0.2
0 1997 1998 1999 2000 2001 2002
Atlanta MSA EIP
Rates per 1000 live births of early-onset group B streptococcal disease (within the first week of life) among infants born in the 20-county Atlanta Metropolitan Statistical Area vs. multi-state data from the CDC's Emerging Infections Program. With over 125,000 live births in Georgia in 2002 and early-onset GBS disease occurring at an annual rate of ~0.4/1000, we estimate that approximately 50 neonatal GBS infections, some of which may have been preventable, occurred statewide.
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Georgia EIP. The response rate was 80% (79/99) for laboratories statewide; 90% (27/ 30) for the 20-county Atlanta Metropolitan Statistical Area (MSA) and 75% (52/69) for the 139 counties of Georgia outside Atlanta (GOA). Seventy-three respondents were hospital-based clinical laboratories, 4 were referral laboratories, and 2 were outpatient clinic laboratories. Ten responding laboratories (13%) served non-obstetrical populations or did not accept specimens for GBS screening, and were excluded from analysis.
Types of GBS Specimens Accepted: Among 69 Georgia laboratories that accepted GBS screening specimens, 19 (28%) accepted only vaginal/rectal swabs, 47 (68%) accepted either vaginal/rectal or cervical swabs, and 3 (4%) accepted only cervical swabs for GBS screening. Vaginal/rectal swabs are recommended for GBS screening, and cervical swabs are not recommended due to reduced sensitivity for detection of GBS colonization. No statistical difference was found in acceptance of cervical swabs between MSA and GOA laboratories (15/ 23, 65% in the MSA vs. 35/46, 76% in GOA).
GBS Specimen Processing: Sixty-seven of 69 laboratories processed GBS screening specimens on-site, and two referred specimens to another laboratory for processing. Fifty-seven of 67 (85%) laboratories processing cultures on-site used a rec-

ommended selective enrichment broth medium (such as LIM or Todd-Hewitt with gentamicin and nalidixic acid) for primary GBS isolation. Use of selective broth medium enhances detection of GBS by 50%, by reducing growth of competing vaginal/rectal organisms. Use of selective broth was more common among MSA laboratories (23/23, 100%) than among GOA laboratories (34/ 44, 77%). Seven GOA laboratories used no enrichment step, and three GOA laboratories used non-selective broth enrichment. Although most of these laboratories served small hospitals, three served hospitals with 199-230 beds, and all 10 laboratories may have missed opportunities to correctly identify GBS-colonized mothers.
Reporting of GBS Growth from Urine Cultures: When reporting urine culture results from women of childbearing age, most laboratories (42/67, 63%) reported all GBS-positive cultures (in any amount), as recommended. However, 12/67 (18%) reported a positive culture only if the GBS colony count was greater than 105 cfu/ml. The remaining 19% of laboratories cited criteria for reporting such as an intermediate colony count or predominance of the organism. The finding of GBS bacteriuria in any amount during pregnancy is indicative of heavy maternal colonization, and is a strong indication for intrapartum antibiotic prophylaxis. In the MSA, 13/23 (57%) reported any GBS growth as recommended, three had intermediate crite-

ria, and 7 reported only if 105 cfu/ml or greater were found. In GOA, 29 of 44 (66%) laboratories reported any GBS growth as recommended, 10 had intermediate criteria, and 5 reported only if 105 cfu/ml or greater were found.
GBS Antimicrobial Susceptibility Testing: Antimicrobial susceptibility testing for GBS isolates was automatically performed by 25% of laboratories (3/23, 13% in the MSA and 14/44, 32% in GOA), and by an additional 49% upon request (13/23, 57% in the MSA and 20/44, 45% in GOA). No susceptibility testing was offered by 13% of laboratories (2/23, 9% in the MSA and 7/44, 16% in GOA). The remainder of laboratories reported selective testing of isolates from women of childbearing age who were known to be penicillin allergic or from all women of childbearing age. Emerging macrolide resistance among GBS organisms necessitates characterization of colonizing GBS isolates when the colonized woman is allergic to penicillin.
Comment: Maternal screening for GBS recto-genital colonization late in pregnancy is now the universally recommended method to target prophylactic intrapartum antibiotic prophylaxis (IAP) for perinatal GBS prevention. Laboratory practices that support and enhance the accuracy of prenatal screening are important

Table 1. Results of 2003 Georgia Emerging Infection Program Laboratory Survey on Group B Streptococcal Screening

Practices

MSA

GOA

Laboratories

Laboratories

N

%

N

%

Question Surveyed

Number of laboratories accepting specimens for GBS culture

23

46

1. What type of specimen(s) does your lab accept for prenatal GBS screens?

Vaginal / rectal swabs*

23/23 100

43/46 93

Cervical swabs

15/23 65

35/46 76

Number of laboratories processing GBS cultures

23

44

2. Which primary enrichment broth medium does your laboratory use for isolation of GBS? Selective enrichment broth* Non-selective enrichment broth No enrichment broth used

23/23 100 0/23 0 0/23 0

34/44 77 3/44 7 7/44 16

3. When does your laboratory report GBS growth from urine from women of childbearing age? Report any GBS-positive growth from urine* Between the two
Reportonlyif> 105 cfu/ml GBS from urine

13/23 57 3/23 13 7/23 30

29/44 66 10/44 23 5/44 11

4. What triggers your lab to test a GBS isolate for antimicrobial susceptibility? Test all isolates automatically/ all from women of childbearing age* Test if requested* Test isolates from penicillin-allergic women of childbearing age* Susceptibility testing not performed * = Preferred answer, consistent with CDC Guidelines
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3/23 13 12/23 52 6/23 26 2/23 9

15/44 34 21/44 48 1/44 2 7/44 16

to optimal GBS prevention. For example, the anatomic source of a GBS screening specimen is of great importance to the accuracy of the test. Use of vaginal/rectal swabs (swab from both vagina and rectum) improves GBS isolation by 40% compared with vaginal specimens alone; and cervical cultures yield 40% fewer positive cultures than single vaginal swabs (ref). The potential for a false-negative screening test due to improper collection is therefore a problem when cervical swabs are accepted. Laboratories that provide feedback to providers who submit cervical swabs or vaginal-only swabs, and inform providers of current recommendations that they submit combined vaginal/ rectal swabs, can improve recognition of pregnancies at risk. Given the limited sensitivity of cervical swabs, this feedback is important to appropriate patient care.
Specimen processing by laboratories can also affect the sensitivity of screening. GBS recovery increases by 50% with use of selective broth enrichment, as compared with nonselective enrichment medium. In Georgia, use of nonselective broth enrichment or no enrichment step was found in several laboratories outside the Atlanta MSA, but not among MSA laboratories. It is possible that outreach and education provided over many years by the MSA active surveillance system may have improved laboratory practices in this regard, and that GOA laboratories may become amenable to the newer guidelines with further effort.
Urine specimens growing GBS in any amount should be reported in women of childbearing age. The presence of GBS in urine suggests high-level colonization of the recto-genital tract, and increased risk for disease in the newborn; this is a strong indication for IAP. Laboratories accustomed to reporting only urine specimens with high level GBS growth will need to

re-address their policies to permit optimal patient management.
Fortunately, all GBS isolates remain susceptible to penicillin and ampicillin, the drugs of choice for GBS prophylaxis, but recommendations for treatment of women with GBS colonization and severe allergy to penicillin pose challenges for providers and laboratories. With the emergence of GBS strains resistant to clindamycin and erythromycin, guidelines recommend susceptibility testing of isolates in these cases. Colonized women at low risk for anaphylaxis should receive cefazolin for IAP, but GBS isolates from women at high risk for anaphylaxis should be tested for susceptibility to both clindamycin and erythromycin to allow correct antibiotic choice. Vancomycin is reserved for women at high risk for anaphylaxis to penicillin who are colonized with a clindamycin- or erythromycin-resistant strain, or if susceptibility is unknown. In Georgia, routine susceptibility testing is not the rule, and in some cases is not available even by request. A likely outcome of this situation is overuse of vancomycin for IAP, a choice that is sub-optimal for prevention of disease as well as promotion of cross-resistant organisms.
Comparing laboratory practices in the Atlanta MSA and GOA provides an opportunity to characterize circumstances that may exist elsewhere in the U.S. As long-term participants in GBS active surveillance through the EIP, and participants in previous GBS surveys, laboratories in the MSA have received more education regarding laboratory practices for prevention of perinatal GBS than laboratories in GOA. Laboratory practices in GOA may more accurately reflect national practices in non-EIP sites. All MSA laboratories are using gold-standard practices for GBS isolation with use of primary selective broth enrichment media, but many of these laboratories continue to accept cervical swabs for processing, and many are not reporting all GBS growth from urine cultures in women of childbearing age. Laboratories

in the MSA and GOA are struggling with ways to provide antibiotic susceptibility testing when indicated. Georgia EIP capacity to conduct active surveillance for perinatal GBS disease throughout Georgia was established in 2004, with the hope that prevention practices can be optimized statewide through case recognition and critical review of prevention practices that were in place to prevent disease.
Limitations of this study include several large hospital laboratories that did not return a survey; one MSA hospital and 5 GOA hospital non-respondents reported deliveries of >1000 infants per year.
Information for clinical microbiologists such as an instructional photo gallery and slide sets, as well as for healthcare providers, health departments and pregnant women, are available at www.cdc.gov/ groupbstrep.
Authors: Jody Schweitzer, M.P.H., Suzanne Segler, M.P.H., Pat Martell-Cleary, M.S.W., L.P.N., Wendy Baughman, M.S.P.H., Katie Arnold, M.D.
Acknowledgmen ts: The authors would like to thank the contributing hospitals and laboratories in our state who made this study possible, and who continue to generously support EIP activities. Many thanks as well to Stephanie Schrag, D.Phil. and Karen Cowgill, Ph.D. from CDC, for assistance with questionnaire development, and to Monica Farley, M.D. of the Georgia Emerging Infections Program for oversight of Georgia EIP activities.
References:
CDC. Prevention of perinatal group B streptococcal disease. MMWR 2002; 51: No. RR-11, 1-24. Schrag S, Zell ER, Lynfield R, et al. A populationbased comparison of strategies to prevent early-onset group B streptococcal diseaes in neonates. NEJM 2002; 347:233-281. CDC. Laboratory practices for prenatal group B streptococcal screening -- seven states, 2003. MMWR 53(23);506-509.

Division of Public Health http://health.state.ga.us
Kathleen E. Toomey, M.D., M.P.H. Director
State Health Officer

Epidemiology Branch http://health.state.ga.us/epi
Paul A. Blake, M.D., M.P.H. Director
State Epidemiologist
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Georgia Epidemiology Report Editorial Board
Carol A. Hoban, M.S., M.P.H. - Editor Kathryn E. Arnold, M.D.
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The Georgia Epidemiology Report Epidemiology Branch Two Peachtree St., NW Atlanta, GA 30303-3186

PRESORTED STANDARD U.S. POSTAGE
PAID ATLANTA, GA PERMIT NO. 4528

November 2004

Volume 20 Number 11

Reported Cases of Selected Notifiable Diseases in Georgia Profile* for August 2004

Selected Notifiable Diseases
Campylobacteriosis Chlamydia trachomatis Cryptosporidiosis E. coli O157:H7 Giardiasis Gonorrhea Haemophilus influenzae (invasive) Hepatitis A (acute) Hepatitis B (acute) Legionellosis Lyme Disease Meningococcal Disease (invasive) Mumps Pertussis Rubella Salmonellosis Shigellosis Syphilis - Primary Syphilis - Secondary Syphilis - Early Latent Syphilis - Other** Syphilis - Congenital Tuberculosis

Total Reported for August 2004
2004 59
2822 35 1 84
1276 8 36 50 3 1 0 0 2 0
288 41 1 6 1 6 0 10

Previous 3 Months Total

Ending August

2002

2003

2004

214

257

180

8723

9296

8844

39

40

63

21

14

2

283

247

240

4939

4726

4000

13

17

21

104

150

79

150

216

169

3

12

13

3

2

4

6

5

2

0

1

0

10

8

4

0

0

0

711

809

820

368

285

167

30

34

9

100

114

42

181

179

17

193

197

63

3

3

0

166

138

68

Previous 12 Months Total

Ending in August

2002

2003

2004

599

700

529

33816

36300

34019

144

118

170

60

31

23

909

868

844

18767

18416

15557

101

78

119

626

550

649

484

612

671

13

35

41

4

11

12

43

33

23

3

2

1

28

32

27

0

0

1

1848

1991

2082

1400

1879

709

100

119

106

302

429

354

719

786

382

794

834

569

19

12

2

620

523

493

* The cumulative numbers in the above table reflect the date the disease was first diagnosed rather than the date the report was received at the state office, and therefore are subject to change over time due to late reporting. The 3 month delay in the disease profile for a given month is designed to minimize any changes that may occur. This method of summarizing data is expected to provide a better overall measure of disease trends and patterns in Georgia.

** Other syphilis includes latent (unknown duration), late latent, late with symptomatic manifestations, and neurosyphilis.

AIDS Profile Update

Report Period
Latest 12 Months: 11/03-10/04 Five Years Ago: 11/99-10/00 Cumulative: 07/81-10/04

Total Cases Reported* <13yrs >=13yrs Total

9

1,790 1,799

10

1,234 1,244

229

28,474 28,703

Percent Female
27.3
28.0
19.0

Risk Group Distribution (%) MSM IDU MSM&IDU HS Blood Unknown

34.0

6.3

2.0

14.1

1.6

42.0

30.5

11.9

3.1

19.7

2.4

32.5

45.9

16.2

5.1

14.4

1.9

16.5

Race Distribution (%) White Black Other

22.2 74.8

3.1

18.8 77.8

3.4

32.5 64.9

2.6

MSM - Men having sex with men

IDU - Injection drug users

HS - Heterosexual

* Case totals are accumulated by date of report to the Epidemiology Section

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