Identification and control of a gentamicin resistant, meticillin susceptible Staphylococcus aureus outbreak on a neonatal unit

Abstract

We describe the identification and control of an outbreak of gentamicin resistant, meticillin susceptible Staphylococcus aureus (GR-MSSA) on a 36-bed neonatal unit (NNU) in London. Control measures included admission and weekly screening for GR-MSSA, cohorting affected babies, environmental and staff screening, hydrogen peroxide vapour (HPV) for terminal disinfection of cohort rooms, and reinforcement of hand hygiene. Seventeen babies were affected by the outbreak strain over ten months; seven were infected and ten were asymptomatic carriers. The outbreak strain was gentamicin resistant and all isolates were indistinguishable by pulsed-field gel electrophoresis. The outbreak strains spread rapidly and were associated with a high rate of bacteraemia (35% of 17 affected patients had bacteraemia vs. 10% of 284 patients with MSSA prior to the outbreak, p=0.007). None of 113 staff members tested were colonised with GR-MSSA. GR-MSSA was recovered from 11.5% of 87 environmental surfaces in cohort rooms, 7.1% of 28 communal surfaces and 4.1% of 74 surfaces after conventional terminal disinfection. None of 64 surfaces sampled after HPV decontamination yielded GR-MSSA. Recovery of GR-MSSA from two high level sites suggested that the organism could have been transmitted via air. Occasional breakdown in hand hygiene compliance and contaminated environmental surfaces probably contributed to transmission.

Keywords: Environmental contamination; MSSA; Staphylococcus aureus; gentamicin-resistance; hydrogen peroxide vapour decontamination; neonatal; outbreak.

Figure 1.

Epidemic curve of gentamicin resistant Staphylococcus aureus on the neonatal unit. Numbers indicate when the various outbreak interventions were implemented Key to interventions:

1. Multidisiplinary outbreak team convened. This group reinforced standard infection control procedures and compliance was monitored by the infection control nurse. Staff and equipment were cohorted along with the babies as far as possible. Mothers of colonised babies used cohorted milk expressing equipment at the cot-side. Empirical antibiotic policy for late onset sepsis changed from amoxicillin plus gentamicin to flucloxacillin plus gentamicin. Admission and weekly screening for GR-MSSA introduced

2. All babies on the unit screened for GR-MSSA. Twice weekly screening for GR-MSSA introduced. Environmental screen of the unit performed. Staff screening performed

3. Hand hygiene finger plating exercise performed

Figure 2.

Secular trend in annual number of patients with any Staphylococcus aureus positive culture on the neonatal unit between 2002 and 2009 GR-MSSA = gentamicin resistant, meticillin-susceptible S. aureus GS-MSSA = gentamicin susceptible, meticillin-susceptible S. aureus MRSA = meticillin resistant S. aureus