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Journal Club

Journal Club. Tiffany Ohta, PL-2 29 Aug 2006. Case. Kari is a 32 y/o G3P2 female who comes in to L&D at 37+1 weeks gestation after ROM 1 hour ago and now with contractions every 5 minutes

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Journal Club

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  1. Journal Club Tiffany Ohta, PL-2 29 Aug 2006

  2. Case • Kari is a 32 y/o G3P2 female who comes in to L&D at 37+1 weeks gestation after ROM 1 hour ago and now with contractions every 5 minutes • Prenatal labs: O+, RPR NR, RI, HepBsAg neg, HIV neg, GBS unknown but negative last 2 pregnancies, negative UA and UCx • Previous 2 pregnancies were uncomplicated SVD’s, has missed some prenatal appts with last appt 3 weeks ago

  3. Case • On exam, membranes found to be grossly ruptured and on cervical exam found to be 8/90%/+1 • Within 5 minutes of being transferred to a labor room, Kari felt the urge to push, and after 5 minutes of pushing, a healthy infant male was born with APGAR’s 9 and 9 weighing 2.9 kg

  4. Case • Since the mother’s GBS status was unknown and did not receive any IAP, the infant was placed on q4 vitals and would be observed for 48 hours per hospital procedure • After 24 hours, the mother became insistent that she wanted to go home as she has 2 other kids at home, and “my mom is an RN, and she will know if anything is wrong with Joey”

  5. Question • Is there a test other than a 48 hour GBS culture that would produce results sooner? YES! • Could this test potentially prevent delayed discharge and reduce costs associated with it? YES! • Let’s evaluate this test further…..

  6. Real Time Polymerase Chain Reaction for the Rapid Detection of Group B Streptococcal Colonization in Neonates Natarajan et al. Pediatrics. 2006; 118; 14-22

  7. What is the big deal about GBS? • A leading cause of morbidity and mortality in newborns, resulting in sepsis, pneumonia, and meningitis • GBS carried in the vaginal and anorectal flora of up to 30% of women – colonization can be intermittent or persistent • Those with GBS bacteriuria are known to be more frequently and more heavily colonized

  8. What is the big deal about GBS? • Colonization rate in newborns born to GBS positive mother is 40-70% • Risk factors for neonatal colonization: • Heavily colonized mother • Vaginal delivery • Prolonged ROM >18 hrs • Preterm delivery • Maternal temp >38°C • Lack of intrapartum antibiotic prophylaxis (IAP)

  9. What is the big deal about GBS? • “Early onset” infection defined as occurring within first 7 days • Incidence is 0.5-3/1000 live births with 4-10% mortality (preemies 20-30%) • Goal of preventive strategies is to reduce or eliminate transmission by giving antibiotics to GBS-colonized women during delivery and selectively giving antibiotics to newborns after delivery • Can reduce early onset GBS rates by 80-95%

  10. GBS unknown… • Occasions when GBS status will be unknown – missed appts, lost specimens, lab errors, or preterm delivery • IAP indicated if GBS status unknown within 6 weeks of delivery and if risk factors develop • Infants are observed for 48 hrs and work-up initiated with antibiotics if s/s concerning for infection or GA <35 wks

  11. GBS rapid testing? • Recent investigation into rapid methods of GBS detection, especially in the laboring women with unknown GBS status • Fluorescent real-time PCR is reported to be highly sensitive and specific in laboring women and gives results in 30-45 min • Not yet used at NNMC

  12. GBS rapid testing? • Currently limited data on the validity of rapid methods of GBS detection in neonates • Could more accurately recognize colonized infants that would need further evaluation and treatment • Could prevent delayed discharge, increased nursing time for frequent vitals, and unnecessary evaluation of those not at risk

  13. Methods – Subject Selection • Study done at Hutzel Women’s Hospital in Detroit from July 2002 to March 2004 • Subjects included neonates >32 weeks GA whose maternal GBS status was unknown • Unknown due to lack of prenatal care, unavailability of results, or PTL <35 wks • Excluded critically ill infants

  14. Methods – Clinical Data • Recorded maternal data: age, race, previous hx of infants with GBS, +/- IAP, presence of GBS bacteriuria, chorio, and duration of ROM • Recorded neonatal data: gestational age, gender, birth wt, results of diagnostic eval if done, +/- antibiotics, course in hospital, duration of hospitalization

  15. Methods - Procedures • Neonates had collection of specimens from 4 locations for both standard cx and PCR (before 1st bath within 4 hrs of delivery) – nares, ear canals, rectum, and gastric aspirate • On culture, GBS identity confirmed by ß-hemolysis on blood agar and serologic grouping

  16. Methods - PCR • LightCycler technology – combines PCR reaction with real-time detection of fluorescently tagged amplified products after each cycle • Technique used to simultaneously amplify and quantify a specific part of a DNA molecule • Positive controls - genomic DNA from 5 commercially available strains of GBS

  17. Methods - PCR • Melting curve was generated for each specimen to confirm the amplified product (All PCR products should have same melting point unless contaminated or other lab error) • All 5 positive controls had identical melting curves, so only one was used to compare to all specimen runs • Gel electrophoresis was also used to confirm the real-time PCR products

  18. Melting Curve

  19. Results – patient characteristics • 94 infants • Mean birth wt 3002g and GA 38 wks • Males 53.2% • CBC/cx done in 47.9% • 26.6% received empiric antibiotics – clinical s/s sepsis or suggestive findings on CBC • No cases of early onset GBS in this cohort • Median duration of stay – 3 days

  20. Results – maternal characteristics • Mean age 25.7, 81.9% black • 24 with chorio • 11 with PROM • 4 with GBS bacteriuria • 3 with h/o previous child with GBS • 22 received IAP for risk factors

  21. Results – rates of colonization • 16 infants (17%) found to be colonized at 1+ sites based on culture • 48 infants (51%) found to be colonized at 1+ sites based on PCR

  22. Results – rates of colonization • Real-time PCR had a higher detection rate when compared to cultures, with ears and nares being best sites for detection • Authors believe the increased detection represents true colonization rather than false positives since “the assay was performed under stringent conditions for specificity, both inherent and imposed”

  23. Results – rates of colonization • Interestingly, among the 22 infants whose mothers received antibiotics, GBS colonization observed in 4 (18.2%) by culture, and 11 (50%) by PCR • Among the infants without exposure to antibiotics, 12 (16.7%) had GBS by culture, and 37 (52.1%) had GBS by PCR • Not statistically significant differences, but authors do comment that the study was NOT powered to evaluate these differences

  24. Are the results valid? • Was there an independent, blind comparison with a reference standard? • YES! • Reference standard is the culture, which was independently evaluated from the PCR results • Did the patient sample include an appropriate spectrum of patients to whom the diagnostic test will be applied in clinical practice? • YES! • Neonates with GBS status unknown mothers

  25. Are the results valid? • Did the results of the test being evaluated influence the decision to perform the reference standard? • NO! • Reference standard and experimental test performed in all patients • Were the methods for performing the test described in sufficient detail to permit replication? • YES! Procedures for cx and PCR very detailed

  26. What are the results? • Are likelihood ratios for the test results presented or data necessary for their calculation included? • Sort of… • Authors state that pt and maternal characteristics/outcomes were compared in groups who had and did not have colonization, by culture and PCR, using t test, x2 test and Fisher’s exact test to determine significance – results of these tests not presented, however data for calculation is included

  27. What are the results? • “Likelihood ratio” is similar to a chi square test, which is what was apparently used in this study to determine significance • Authors do report specificity, sensitivity, PPV, and NPV • Having a high sensitivity and NPV are crucial to a good screening test

  28. What are the results? ▪ Negative predictive value is consistently high (with narrow CI’s) for all sites, which is especially useful when evaluating a screening test

  29. What are the results? • Sensitivity is another important measure for a screening test – a very sensitive test produces few false negatives • PCR had high sensitivity for the ear and nose sites, however the CI’s were wide • Sample size in this study is low (94) – increasing the sample size could decrease the standard error, which would narrow the CI and also increase the power

  30. Will the results help me in caring for my patients? • Will the reproducibility of the test result and its interpretation be satisfactory in my setting? • YES – results easily interpreted and reproducible • Are the results applicable to my patient? • YES – common occurrence to have an infant with a GBS status unknown mother

  31. Will the results help me in caring for my patients? • Will the results change my management? • YES – advantages are that the test is noninvasive, easy to perform, and quick • Based on this study, ~50% of infants born to GBS unknown mothers are negative for GBS – this group could potentially need no additional testing or observation • However, preemies 32-35 weeks likely still do full eval/observation in most circumstances

  32. Will the results help me in caring for my patients? • Cost-benefit? • PCR test $26 (16-54) • Maternal prenatal culture $21 • Maternal antibiotic prophylaxis $63 (30-115) • In hospital care of well infant $1100 (500-1500) • NICU care of GBS infant $30100 (12000-128000) • Primary goal would be to decrease hospital stay and nursing care

  33. Will the results help me in caring for my patients? • Will patients be better off as a result of the test? • YES – prevent delayed discharge, decreased interventions in the immediate neonatal period, decrease costs

  34. Questions?

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