Pediatr Infect Vaccine.  2019 Dec;26(3):148-160. 10.14776/piv.2019.26.e23.

Molecular Epidemiologic Study of a Methicillin-resistant Staphylococcus aureus Outbreak at a Newborn Nursery and Neonatal Intensive Care Unit

• Kang HM
• Park KC
• Lee KY
• Park J
• Park SH
• Lee DG
• Kim JH

• KMID: 2466459
• DOI: http://doi.org/10.14776/piv.2019.26.e23

Abstract

PURPOSE
This study aimed to investigate the molecular epidemiology of a methicillin-resistant Staphylococcus aureus (MRSA) outbreak at a newborn nursery and neonatal intensive care unit (NICU).
METHODS
During the outbreak, from August to September 2017, MRSA isolates collected from neonates and medical staff underwent genotyping and screened for virulence factors. Antibiotic susceptibilities were tested.
RESULTS
During the study period, 41 neonates were admitted at the nursery (n=27) and NICU (n=14). Of these, 7 had MRSA infections (skin infection [n=6] and sepsis [n=1]) and 4 were colonized with MRSA. Associated medical staff (n=32) were screened; three were nasal MRSA carriers. Staphylococcal chromosomal cassette mec (SCCmec) type II, sequence type (ST) 89, spa type t375 was found to be the skin infection outbreak causing strain, with multi-drug resistance including low-level mupirocin resistance. SCCmec type IVa, ST 72, and a novel spa type designated t17879, was the cause of MRSA sepsis. Many different types of MRSA were colonized on the neonates; however, SCCmec type IVa, ST 72, spa type t664 was colonized in both neonates and a NICU nurse. All MRSA isolates from colonized infants were positive for the Panton-Valentine leukocidin (PVL) toxin gene.
CONCLUSIONS
The strain causing an outbreak of skin infections had multi-drug resistance. Also, MRSA colonized in the neonates were found to carry the PVL toxin gene. Because different strains are present during an outbreak, molecular epidemiologic studies are important to identify the outbreak strain and colonized strains which aid in effective control and prevention of future MRSA outbreaks.

Keyword

Neonate; Methicillin-resistant Staphylococcus aureus; Transmission; Disease outbreaks

MeSH Terms

Colon
Disease Outbreaks
Drug Resistance, Multiple
Epidemiologic Studies*
Humans
Infant
Infant, Newborn*
Intensive Care, Neonatal*
Leukocidins
Medical Staff
Methicillin Resistance*
Methicillin-Resistant Staphylococcus aureus*
Molecular Epidemiology
Mupirocin
Nurseries*
Sepsis
Skin
Virulence Factors
Leukocidins
Mupirocin
Virulence Factors

Figure

• 

  Fig. 1 Timeline of the discovery of MRSA skin infections and colonizers. Patients with MRSA infections (square icon) and colonization (circle icon) are shown on the timeline. Their initial admission periods are shown as arrows. Patient C and D's MRSA isolates were not collected. Patients A-F had skin infections, and patient L was diagnosed with MRSA sepsis. Intervention included strict hand hygiene, cohorting of MRSA positive patients, and MRSA eradication by mupirocin oint application. Abbreviations: MRSA, methicillin-resistant Staphylococcus aureus.

• 

  Fig. 2 ileS gene sequence and chromatogram image of MRSA isolates with low-level mupirocin resistance showing missense mutation. The gene sequence of the ileS gene of the outbreak strains (samples No. 4, 5, 7, and 8) showed a G→T point mutation at the 1852 position, resulting in an amino acid change from valine to phenylalanine (V588F) in the region of the Rossman fold of the isoleucine synthetase where mupirocin binds (S. aureus ileS gene sequence was obtained from PubMed GenBank accession No. X74219.1). Abbreviations: ileS, isoleucyl-tRNA synthetase; MRSA, methicillin-resistant Staphylococcus aureus.

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