BACKGROUND: Group B streptococcus (GBS) infection is a leading cause of neonatal morbidity and mortality worldwide. Here, we present the analytical and diagnostic usefulness of a new real-time PCR-based assay (Xpert GBS; Cepheid, USA) for rapid and accurate prenatal GBS screening. METHODS: We enrolled 175 pregnant women who were between 35 and 39 weeks of gestation. The analytical performance of the Xpert GBS assay was first tested using a reference GBS strain. Next, to test diagnostic performance, rectovaginal swabs were obtained from pregnant women who visited the hospital for regular antenatal screening after 34 weeks of gestation. The results of the Xpert GBS assay were compared to those of standard culture for the detection of prenatal GBS colonization. RESULTS: When any positive result from Xpert GBS or culture was considered a true positive, the sensitivity of the Xpert GBS assay and culture were 91% (20/22; 95% CI [confidence interval], 72-98) and 68% (15/22; 95% CI, 47-84), respectively. The specificity of both methods was 100% (153/153; 95% CI, 97-100). The sensitivity and specificity of the Xpert GBS assay, using the culture results as a reference, were 86.7% and 95.6%, respectively. In the Xpert GBS assay, the median threshold cycle of vaginally colonized samples was significantly lower than rectally colonized samples (P<0.01). CONCLUSIONS: The Xpert GBS assay is an accurate, rapid, easy-to-use test for the detection of maternal GBS colonization in prenatal screening that might be especially useful in clinical settings where standard culture is not feasible.
DNA, Bacterial/*analysis ; Female ; Gestational Age ; Humans ; Pregnancy ; Pregnancy Complications, Infectious/*diagnosis/microbiology ; Prenatal Diagnosis ; Reagent Kits, Diagnostic ; Real-Time Polymerase Chain Reaction ; Rectum/microbiology ; Sensitivity and Specificity ; Streptococcal Infections/*diagnosis/microbiology ; Streptococcus agalactiae/*genetics/isolation & purification ; Vagina/microbiology

OBJECTIVETo establish a methed of cleavage fragment length polymorphism (CFLP) analysis with a primer labeled at the 5'-end with digoxigenin for genotyping of Chlamydia trachomatis (Ct). The methods for detection of Ct by major outer membrane protein (MOMP) gene (ompl) with nested polymerase chain reaction (ompl-nPCR) were studied. The incidence of Ct infection in pregnant women, the common genotypes and vertical transmission rate of Ct in Chongqing area during the past one year was also investigated.

METHODSThe samples were taken from cervical scrapes of parturient women and nasopharygeal swabs of their neonates from April 2003 to Feb. 2004 in Chongqing Women and Children's Health Care Institute. Totally 300 pairs (605 specimens) were detected by using ompl-nPCR, ompl-PCR (inside pair of primers was used directly) and plasmid-PCR. The results were judged by the modified gold standard (MGS). The ompl-nPCR amplified DNA was purified by recovery of DNA from agarose gel electroelution into dialysis bags. The DNA amplified from ompl-nPCR was sequenced by ABI PRISM 377 DNA sequencer. CFLP assay with a primer labeled at the 5'-end with digoxigenin was created for genotyping of Ct, and was primarily applied.

RESULTSThe minimum detectable levels of ompl-nPCR and ompl-PCR corresponded to 2.5 elementary body (EB) and 25 EB, respectively. The sensitivity of ompl-nPCR was 10 times that of ompl-PCR. The positive rate of Ct in the samples from the pregnant women was 11% (33/300). The vertical transmission rate of Ct from mothers to their infants was 24.2% (8/33). The rate of Ct isolated from nasopharyngeal swabs 5 - 10 days after birth was 38.9% (7/18), which was significantly greater than that [3.0% (1/33)] detected within 24 hours after birth (chi(c)(2) = 8.79, P < 0.01). Of the 33 Ct-positive samples from pregnant women, 9 had vaginal delivery and 24 had caesarean section. The vertical transmission rates in vaginal delivery group and caesarean section group were 66.7% (6/9) and 8.3% (2/24), respectively (chi(c)(2) = 9.16, P < 0.01). Incidence of premature rupture of membrane in Ct-positive group was 30.3% (10/33), which was greater than that of Ct-negative groups (13.5%, 36/267, chi(2) = 6.40, P < 0.05). Four different patterns were observed in the 16 Ct-positive samples from 8 pregnant women and 8 matched maternal-infants by using CFLP, which were confirmed by DNA sequencing later. They were type E (3 pairs), type F (2 pairs), type H (2 pairs) and type D (1 pair). Each pair of matched maternal-infantile samples presented identical CFLP pattern.

CONCLUSIONSThis study revealed the infection rate of Ct in pregnant women, vertical transmission rate of Ct and the common genotypes of Ct in Chongqing Women and Children's Health Care Institute. The CFLP assay by using a primer labeled at the 5'-end with digoxigenin was first used for genotyping of Ct. The assay showed a good sensitivity and reproducibility, no radioactive contamination, and is simple. Therefore the assay is a potential new method for Ct genotyping.

Cervix Uteri ; microbiology ; Chlamydia Infections ; diagnosis ; Chlamydia trachomatis ; genetics ; DNA Primers ; Female ; Genes, Bacterial ; genetics ; Genotype ; Humans ; Polymerase Chain Reaction ; Polymorphism, Genetic ; Pregnancy ; Pregnancy Complications, Infectious ; diagnosis