Methods
Institutional review board and patient consent.
The PREVALANCE-in-TAJIMR study was approved by the Institutional Review
Board of Toyooka Public Hospital (Permission number:109). Written
consent was obtained from each pregnant woman for her and her neonate’s
participation in the study.
Study design, study period and study participants
The Prevalance-in-TAJIMR study is an observational, prospective cohort
study in the TAJIMA area, which is the northern area of the Hyogo
Prefecture in Japan. Pregnant women at 32 to 36 weeks gestation who
visited the Perinatal Medical Center in Toyooka Public Hospital were
recruited from August 2016 to December 2017. Women who were
>18 years of age, willing to comply with the study-related
procedures (including nasal swabs, enrollment of her child at birth),
and capable of providing written informed consent were enrolled. At the
time of enrollment, moistened nasal and vaginal swabs were collected
from the mother. Mothers and their neonates were followed until day
seven after birth and were assessed of adverse outcomes. MRSA-positive
women and their neonates were separately monitored during
hospitalization.
Although MRSA can be detected in various sites, they are commonly
detected in the nares9,10. In addition, we were
interested in how often MRSA can be detected in the vagina. Therefore,
we screened for maternal MRSA colonization using nasal and vaginal
samples in our study. For neonates, we used nasal and umbilical samples
for screening, as these sites had the highest detection efficiency
according to the previous reports9,10.
Data collection at enrollment
The clinical data were collected from our medical records and through
in-person interview questionnaires. We collected factors related to
maternal background, including maternal age at enrollment, body mass
index (BMI), parity, occupation (healthcare provider or not), history of
spontaneous abortion, history of infertility treatment, diagnosis of
preterm labor at enrollment, usage of antibiotics during current
pregnancy, twin pregnancy, diagnosis of gestational diabetes mellitus
(GDM) before enrollment, diagnosis of hypertensive disorders of
pregnancy (HDP) before enrollment, regular hospital visits outside of
regular prenatal examinations, alcohol consumption, smoking history,
surgical history, hospitalization during pregnancy, and colonization of
GBS in the rectovaginal region.
Study outcomes
The primary outcome of this study was to determine the prevalence of
neonatal MRSA colonization at birth. In addition, we investigated the
cumulative incidence of both maternal and neonatal events that occurred
in the perinatal period as the secondary outcome. We investigated the
following maternal events: preterm delivery before 37 weeks of
gestation, cesarean section (C/S), premature rupture of the membranes
(PROM), prolonged PROM duration (over 24 hours), and vacuum or forceps
delivery. We investigated the following neonatal events: pH of the
umbilical cord arterial blood, Apgar score (1 minute and 5 minute),
fetal weight, admission into the NICU, and development of SSTIs, which
may be less serious but are potentially associated with MRSA.
Sample collection and MRSA detection
All samples were collected using a standardized sterile procedure by
midwives and doctors at enrollment and during delivery. In our hospital,
the midwives or doctors involved in labor and delivery always applied
sterile techniques when touching pregnant women and fetuses, so the
specimens collected immediately after delivery are completely unaffected
by the delivery personnel. Therefore, if MRSA is detected in the
cultures of the fetal samples collected immediately after delivery, it
should be considered that the infection is almost entirely due to
vertical transmission.
All samples collected in this study were processed at Toyooka Public
Hospital. We used a cotton-tipped seed swab γ1 (Eiken Chemical Co., Ltd.
Tokyo, Japan). Within 24 hours after collection, the swabs were streaked
on MS-CFX MRSA-specific agar plates, which consisted of mannitol salt
agar with egg yolk supplemented with cefoxitin (Nissui, Tokyo, Japan),
and the plates were incubated for 24 to 48 hours in ambient air at 35°C.
Data analysis
Chi-square test or Fisher’s exact test was used to examine the
associations in categorical variables and unpaired t-test was used to
examine the associations among continuous variables. Multivariable
logistic regression model was used to determine the independent
predictors of the primary outcome (neonatal MRSA colonization) and
secondary outcomes. Statistical significance was considered if
p<0.05. Odds ratios (ORs) and 95% confidence intervals (95%
CI) were calculated and a variable was considered significantly
associated with the outcomes if the CI did not include 1.0. Details
about statistics method are described in Supplementary material, Method
S1.