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Re: beta strep screeningFrom: Terrence.Jones@ncal.kaiperm.orgThu Nov 7 15:31:51 1996
Mitch, since the other PITA's are sounding off, let me ask -- were the Mom's who were cultured at 35-7 weeks and tested negative for GBS, only to go on and deliver very ill GBS septic newborns; cultured with selective media, with appropriate transport media, and with rectal source included? The yield for GBS drops when Todd-Hewitt (naldixic acid/gent/sheep blood) is deferred. (False neg rate close to 50%). The guidelines specify 'selective media', and even suggest transport policy (delayed inoculation drops the detection rate from 95% to 83%.). With selective media, the detection rate with vaginal (not cervical - which would be lower) c/s = 59%, for rectal c/s90%, and both sites = 100%. The Silver & Struminski paper (Prov R.I.) from July '96 AJOG (vol 175:155-7) mentions, in the 'Material & methods', "there is currently only one commercially available prepackaged tube containing Todd- Hewitt broth, and the tube is GLASS, decreasing its value as a transport tube." These investigators used a bit of innovation to prepare their own sterile plastic selective direct inoculation tubes and did a cost-analysis comparison. (Incidentally the Boyer study - NEJM 1986 {324:1665-9} - upon which the AAP based their 28 wk screening recc's, used direct inoculation onto selective growth media technique.) For clarification purpose (as well as making a new paragraph in case Mats is reading), the policy was not designed to avoid all intrapartum GBS sepsis. The June 1996 ACOG comm opinion (pg 10, bottom left) describes the efficacy of the two strategies, and the associated chemoprophylaxis treatment burden. Late prenatal cultures will treat 27% of pts and prevent 86% early onset GBS. Using risk factor strategy will treat 18% and prevent 68% EARLY ONSET GBS. I'm not sure if it was You, or Joe (the man), or WHO? mentioned it - but someone pointed out a few months back -- these strategies are aimed at intrapartum prophylaxis of EARLY ONSET sepsis, some babies are already quite ill on presentation. The pediatric meningitis lit in the recent past is looking at cytokine-mediated neural damage - in some cases the bacterial burden is so great that the inflammatory response upon initiating antibiotic therapy not only seals the fate, but may hasten it. (Interestingly, they're looking at steroids - but that's another topic.) It seems the best we can do is remain aware of what we are aiming therapy at with intrapartum prophylaxis. To be aware of the pitfalls in diagnosis and utilize optimal culture practices when this strategy is chosen. And try and find ways to improve things, when we can. For example, the Mclaren study from Illinois (AJOG 6/96, vol 174:1934-37) tried to fine-tune their assignment of risk factors. They analyzed 21 cases of GBS sepsis from a catchment of 9 hospitals over an 18 month period. The denominator was 10,021 for an incidence of 2.1/1000. Dx based on positive cultures in CSF/Urine/Blood accomp by need for fluid or dopamine for maintaining bp. Only 2 of the 21 (10%) met the CDC criteria for risk factor chemoprophylaxis. When they reduced the interval of ROM to greater than 10 hrs (instead 18 hrs), they were able to pick up 13/21 cases. This then compares favorably to the 0.5/1000 incidence of GBS sepsis in the group undergoing antenatal culture and intrapartum abtc protocol. Of course, flavoring apple Odwalla with ampicillin's no panacea, as it won't be long before bacterial resistance and anaphylaxis begins to show up on our list. But to throw an idea out ("no 'Mr Bill', not the trashbin"...) has anyone considered an algorithm based on population prevalence? For instance, in sites where GBS has replaced the lactobacillus as 'nml flora' would culture strategy be best. While those with rare cases, or in whom less than optimal culture protocols might be subject to litigious scrutiny, perhaps risk factor strategies might prevail? Whatever the decision, keep in mind these strategies are allowing more than half of at-risk infants the opportunity to enjoy their first wks at home with their parents, rather than in the NICU. Someday we'll better define "at risk", and help even more. Anyone interested in Cerebral Palsy, periventricular leukomalacia, and CNS infection, as related to IL-6, TNF-a, and Il-1b mediated coagulative necrosis in CNS white matter see Yoon AJOG 174:1433. T Jones.
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