Community-Acquired Methicillin Resistant Staphylococcus Aureus Colonization in Pregnant Women and Infections in Newborns

Background:

Community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging
pathogen of the 21st century whose incidence as a cause of local and invasive infections has
significantly increased, especially in previously healthy term and near term neonates where
it may be associated with high morbidity and mortality(1, 2, 3). The etiology for this
increase remains unclear, but may be a consequence of perinatal or postnatal acquisition via
maternal transmission through skin, breast milk, or vaginal colonization(4).

The major goals of our study are: to determine the incidence of pregnant women who are
colonized with CA-MRSA, gain a better understanding of the transmission dynamics of this
organism between the mother and the newborn infant, and to develop strategies for the
prevention of transmission, spread and infection with this organism in both these
populations.

This staged study is a collaborative effort between investigators from the Children's
Memorial Hospital Division of Infectious Diseases, Northwestern Memorial Hospital Department
of Obstetrics and Gynecology, and the Northwestern Memorial Hospital Division of Infectious
Diseases. Collaboration across multiple specialties provides strength to the study by
allowing the investigators to address multiple issues that are pertinent to both the care of
pregnant mothers and newborn infants in the inpatient and outpatient setting.

Hypothesis:

1. The incidence of previously healthy term and near-term neonates infected with CA-MRSA
skin & soft tissue (SSTI) and invasive infections is higher in those born to mothers
vaginally and/or nasally colonized with CA-MRSA and, 2. Pregnant women vaginally and/or
nasally colonized with CA-MRSA are at higher risk for post-partum infection with this
organism.

Specific Aims:

1. To determine the incidence of nasal and vaginal colonization with CA-MRSA in pregnant
women and determine the clonality of these strains.

2. To study CA-MRSA transmission dynamics and evaluate the incidence of SSTI and invasive
infections in term and near-term newborns born to S. aureus vaginal and/or nasal
colonized mothers.

3. To study the efficacy of attempted decolonization in CA-MRSA colonized mothers in
decreasing the incidence of transmission and development of SSTI and invasive
infections in their infants during the first month of life.

Methods:

1. Vaginal and anterior nasal cultures will be obtained prospectively over several months
from pregnant women who obtain their prenatal care through Obstetrical practices at
Prentice Women's Hospital and Maternity Center of Northwestern Memorial Hospital during
the time of GBS screening at 34-36 weeks gestation. Together, these practices account
for 300-500 deliveries per month.

2. Cultures will be plated on blood agar and incubated at 37oC for 48 hours. S. aureus
strains will be identified by colony morphology and latex agglutination. MRSA isolates
will be identified by PCR or latex agglutination for penicillin binding protein 2a by
detecting the mecA gene and clonality by PFGE. PCR testing will then be used to
identify strains carrying the Panton-Valentine Leukocidin gene as a marker of
virulence.

3. In a prospective case-control cohort study, newborns born to CA-MRSA colonized mothers
will have anterior nares cultures for S. aureus obtained at birth and followed for the
development of SSTI and invasive infections for one month. Samples positive for MRSA
will be tested for similarities to maternal isolates through methods described above.
The newborn incidence of MRSA infection will be compared between those born to
non-colonized mothers and those born to colonized mothers.

4. In further stages of this study, women found to be nasally and/or vaginally colonized
with CA-MRSA will be randomized to receive postpartum, either: 1) attempted
decolonization with intranasal mupirocin with or without diluted chlorhexidine or
Clorox baths or, 2) no intervention.

Potential Impact:

Understanding the epidemiology of the transmission dynamics of CA-MRSA in previously healthy
neonates will provide important information to support the development of strategies aimed
at the interruption of transmission and prevention of infection caused by CA-MRSA in this
patient population, as well as in pregnant women. This will also allow for the development
of infection control strategies in the hospital setting to prevent the spread of this
organism among post-partum units and nurseries.

Inclusion Criteria:

- Healthy pregnant women who present for routine OB/GYN care during the of the 34-36
week gestation GBS screening visit.

- Healthy term and near-term infants born to these mothers

Exclusion Criteria:

- Pre-term infants

- Infants who had significant illness after birth, i.e. transferred to neonatal
intensive care unit for significant illness.

Age limits for infants will be 0-4 weeks of age and both genders will be included.