Jennifer R. Verani, M.D.
Office of Infectious Diseases
Centers for Disease Control and Prevention
1600 Clifton Road
Atlanta, GA 30333
Dear Dr. Verani:
Thank you for the opportunity to review the Center for Disease Control and Prevention’s (CDC) draft revised guidelines for the Prevention of Perinatal Group B Strep (GBS) Infection. The American Society for Microbiology’s Committees on Laboratory Practices and Professional Affairs reviewed the laboratory portion of the draft and submit the following comments for your consideration:
- Page 12: Line 18 of the draft revised guidelines states “presence of ampicillin-resistant gram sculture (86).” The ASM recommends that this statement be clarified; if the word is supposed to be “culture” the statement is still unclear.
- Page 19: The ASM greatly appreciates the committee addressing the issue of looking for any amount of GBS in urine from pregnant women or women of child-bearing age. As noted in the draft revised guidelines on page 19, this is difficult for laboratories for the reasons you have listed and is not supported by literature. However, on a related issue, we have some concerns about your recommendation for: “Identification of > 104 colonies of GBS from urine specimens from pregnant women with heavily mixed (> 3) organisms ….”.
a) No source/reference is given for this recommendation.
b) Is there literature to support that mixed urine cultures from pregnant women with > 104 cfu/ml of GBS as well as 2 or more other uropathogens or contaminants are a significant factor which will lead to newborn disease?
c) The recommendation to report GBS in mixed urine cultures represents increased workload for clinical microbiology laboratories that generally do not distinguish and report bacterial growth in urine specimens that grow > 3 organisms (i.e., contaminated specimens). Special work up for GBS in urine specimens that are contaminated with mixed fecal flora from all women of reproductive age is contraindicated and may lead to inappropriate antibiotic therapy and increased cost, and potentially expose the patient to an unwarranted risk of drug toxicity while exerting pressure for the development of avoidable antibiotic resistance.
d) As previously stated in the draft revised guidelines, it is true that laboratories rarely know whether urine samples are from pregnant women; as a result, the vast majority of laboratories would need to identify all possible streptococci (beta-haemolytic and non-haemolytic) for the possibility of GBS in all mixed urine cultures from all women of reproductive age (and reproductive age has not been defined).
We submit that the references cited in support of routine screening for asymptomic bacteriuria in pregnant women utilize significant quantities of uropathogens AND clinical significance to the number of organisms growing, i.e., liberally, 2 potential pathogens in a urine culture each at a quantity of > 104cfu/ml. If data exists to show similar clinical importance of mixed urine cultures, it should be stated in the new guidelines. If such data does not exist, the guidelines should limit routine screening to clinically significant culture results as defined by each laboratory or as defined in the 2009 Cumitech on Laboratory Diagnosis of Urinary Tract Infections (already referenced in your guideline).
- Page 24: The guidelines states that “Enrichment is a time-consuming process…”. Enrichment does require 18-24 hours incubation time (as described in the revised draft guideline), but culturing swab specimens into enrichment broth is not ‘time consuming.’
- Page 24: The statement on page 24, “The additional time required for enrichment of samples makes it not feasible for intrapartum testing, and the sensitivity of assays in the absence of enrichment is not adequate in comparison to culture”, does not coincide with the previous review of data/studies on the bottom page 23. Page 23 states: “Two of the studies found intrapartum NAAT to be slightly more sensitive (95.8 and 90.7 %) than antepartum culture (83.3 and 84.3 %, respectively) (177, 180), although with widely overlapping confidence intervals. One study reported a statistically significant difference between NAAT sensitivity (94.0%) and that of antepartum culture (54.3%) (174 ).” The ASM recommends that CDC modify or clarify these statements so that they are consistent and/or allow users to choose NAAT as a test of choice in their own institution if a woman presents in labor without previous testing.
- Page 35 Key components of the strategy: The ASM recommends adding additional information/detail to the first bullet point (women negative for GBS in the urine); we recommend inserting the following language, which is stated earlier in the revised draft document: “Identification of > 104 colonies of clinically significant GBS from urine specimens from pregnant women.”
Thank you again, for the opportunity to comment. Please let us know if ASM can provide any further clarification.
Susan E. Sharp, Ph.D., Chair, Committee on Laboratory Practices
Public and Scientific Affairs Board