Prevalence And Risk Factors Of Nasal Colonization Of Staphylococcus Aureus Among Pregnant Women

Objective To providing scientific basis for preventing postpartum and neonatal infection by understanding prevalence of nasal colonization of Staphylococcus aureus(S.aureus)and methicillin-resistant Staphylococcus aureus(MRSA),exploring influencing factors and revealing molecular characteristic of isolates.Methods We conducted a cross-sectional study and enrolled pregnant women admitted to Longhua central hospital and Guanlan peoples’ hospital to delivery between August and November in 2015 by convenience sampling method.Epidemiologic information was obtained by self-designed questionnaire while nasal swabs were collected.Isolates culture and identification was performed according to a series of standard methods.Formal antimicrobial susceptibility testing was performed on all S.aureus isolates by the Kirby-Bauer disk diffusion method of Clinical and Laboratory Standards Institute guidelines.All S.aureus isolates were tested to confirm the presence of gene including 16 S r RNA,nuc,mec A,pvl,eta,etb and tst gene by adopting several PCR assays.Another multiplex PCR assay was carried out to type the staphylococcal cassette chromosome mec(SCCmec)gene of all MRSA isolates.The multilocus sequence typing(MLST)analysis was performed on all S.aureus isolates.Data analysis was performed using stata 13.0 software.The univariate analysis of risk factors,comparison of drug resistance rates between MRSA and MSSA,and comparison of drug resistance rates between MDR and non-MDR was performed with Pearson’s chi-squared test and Fisher’s exact test.Logistic models were constructed to multivariable analysis.Dendrogram analysis was performed by using e BURST algorithm and dendrogram software to determine the clonal relatedness and potential epidemiologic origin.Result Demographics A total of 2172 mothers agreed to participate to this study with average age 27.74±4.69.89.72% of participants were nonlocal register.House wife accounted for 25.99%,workers and farmer for 16.98%,health care workers for 1.48%,civil servant for 35.11%,service personnel for 9.34%,individual businessman and other for 11.10%.Prevalence of S.aureus and MRSA colonization and risk factors Prevalence of S.aureus and MRSA colonization was 25.60% and 5.62%,respectively.In univariate analysis,BMI prior to conception was statistically associated with S.aureus nasal colonization(P=0.004).Multiple logistic revealed that underweight(BMI<18.5)increased the odds of S.aureus nasal colonization(OR=1.28,P=0.027,95%CI:1.03-1.60).Risk of S.aureus nasal colonization among house wife was 1.40 times than workers and farmers(OR=1.40,P=0.035,95%CI:1.02-1.91).Occupation was statistically associated with nasal colonization of MRSA in univariate analysis(P=0.005).Risk of MRSA nasal colonization among house wife was 2.19 times than workers and farmers(OR=2.19,P=0.009,95%CI:1.21-3.96).Participants who had family member working in medical institutions had 3.38-flod risk of MRSA nasal colonization than participants who did not.Antibiotic resistance pattern of S.aureus In all 556 S.aureus isolates,the highest drug resistance rate was observed in penicillin(91.91%),followed by erythromycin(37.23%)and tobramycin(21.22%).The highest drug resistance rate in MRSA isolates was observed in cefoxitin(97.54%),followed by erythromycin(70.49%)and clindamycin(54.10%).The highest drug resistance rate in MSSA isolates was observed in penicillin(90.32%),followed by erythromycin(27.88%)and tobramycin(21.20%).Resistance rates of clindamycin,erythromycin,rifampicin,cefoxitin and penicillin in MRSA isolates were statistically higher than MSSA isolates(P<0.05).Resistance rates of all antibiotic in MDR isolates were statistically higher than non-MDR isolates(P<0.05).Molecular characteristic Detection rate of pvl,eta,etb,tst genes in S.aureus isolates was 4.50%,2.70%,0.18% and 2.34%,respectively.Carriage of pvl gene in MRSA isolates(11.48%,14/122)was statistically higher than MSSA(2.53%,11/434).Proportion of SCCmec type Ⅱ,Ⅲ,Ⅳ in MRSA isolates was 6.56%,10.66% and 51.64%,while 38 isolate(31.15%)were non-typeable.There were 84 ST types in 556 S.aureus isolates.Isolates primarily belonged to ST188(20.68%,115/556),followed by ST7(9.35%,52/556),ST6(7.73%,43/556).MRSA isolates primarily belonged to ST59(27.05%,33/122),followed by ST45(9.84%,12/122),ST188(9.84%,12/122)and ST7(7.38%,9/122).MSSA isolates primarily belonged to ST188(23.73%,103/434),followed by ST7(9.91%,43/434)and ST6(8.99%,39/434).84 ST types were assigned to 16 international clonal complex(CC5、CC7、CC10、CC12、CC20、CC22、CC30、CC45、CC59、CC88、CC121、CC882、CC398、CC672、CC1719 和 CC2483)with 5 singletons(ST1046、ST198、ST1922、ST2540 和 ST2990).According to the dendrogram analysis,cluster occurred between HA-MRSA and CA-MRSA.Conclusions The status of nasal colonization of S.aureus and MRSA among pregnant women admitted to delivery was rather serious.Underweight was the risk factor of S.aureus nasal colonization.Family member working in medical institution was risk factor of MRSA nasal colonization.House wife were the risk factor of S.aureus and MRSA nasal colonization.Isolates were highly resistant to some antibiotic and status of multi-resistance was rather serious.Colonization of toxic genes among isolate was low.There were various ST types in S.aureus isolates with ST188 being the predominant ST type.There existed potential of intertransmission between HA-MRSA and CA-MRSA.