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

Genomic and Epidemiological Features of Two Dominant Methicillin-Susceptible Staphylococcus aureus Clones from a Neonatal Intensive Care Unit Surveillance Effort

Methicillin-susceptible Staphylococcus aureus (MSSA) is a more prevalent neonatal intensive care unit (NICU) pathogen than methicillin-resistant S. aureus (MRSA). However, the introduction and spread of MSSA, the role of systematic decolonization, and optimal infection prevention and control strategies remain incompletely understood. We previously screened infants hospitalized in a university-affiliated level III to IV NICU twice monthly over 18 months for S. aureus colonization and identified several prevalent staphylococcal protein A (spa) types. Here, we performed whole-genome sequencing (WGS) and phylogenetic comparisons of 140 isolates from predominant spa types t279, t1451, and t571 to examine possible transmission routes and identify genomic and epidemiologic features associated with the spread of dominant clones. We identified two major MSSA clones: sequence type 398 (ST398), common in the local community, and ST1898, not previously encountered in the region. ST398 NICU isolates formed distinct clusters with closely related community isolates from previously published data sets, suggesting multiple sources of acquisition, such as family members or staff, including residents of the local community. In contrast, ST1898 isolates were nearly identical, pointing to clonal expansion within the NICU. Almost all ST1898 isolates harbored plasmids encoding mupirocin resistance (mupA), suggesting an association between the proliferation of this clone and decolonization efforts with mupirocin. Comparative genomics indicated genotype-specific pathways of introduction and spread of MSSA via community-associated (ST398) or health care-associated (ST1898) sources and the potential role of mupirocin resistance in dissemination of ST1898. Future surveillance efforts could benefit from routine genotyping to inform clone-specific infection prevention strategies. IMPORTANCE Methicillin-susceptible Staphylococcus aureus (MSSA) is a significant pathogen in neonates. However, surveillance efforts in neonatal intensive care units (NICUs) have focused primarily on methicillin-resistant S. aureus (MRSA), limiting our understanding of colonizing and infectious MSSA clones which are prevalent in the NICU. Here, we identify two dominant colonizing MSSA clones during an 18-month surveillance effort in a level III to IV NICU, ST398 and ST1898. Using genomic surveillance and phylogenetic analysis, coupled with epidemiological investigation, we found that these two sequence types had distinct modes of spread, namely the suggested exchange with community reservoirs for ST398 and the contribution of antibiotic resistance to dissemination of ST1898 in the health care setting. This study highlights the additional benefits of whole-genome surveillance for colonizing pathogens, beyond routine species identification and genotyping, to inform targeted infection prevention strategies.

Healthcare worker associated outbreak of Panton-Valentine Leucocidin producing meticillin-sensitive Staphylococcus aureus in a large Neonatal Unit in London: successful targeted suppression therapy following failure of mass suppression therapy

BACKGROUND

Staphylococcus aureus is a leading cause of healthcare associated infection and outbreaks have been associated with neonatal units and colonisation of healthcare workers.

AIM

To describe an outbreak of Panton-Valentine Leucocidin producing meticillin-sensitive Staphylococcus aureus (PVL-MSSA) in a Neonatal Intensive Care Unit (NICU).

METHODS

Multi-disciplinary outbreak control investigation RESULTS: Over a period of 16 months, 7 neonates were identified as positive for PVL-MSSA. Isolates were identified in blood cultures (2 patients), nasopharyngeal aspirate (1 patient) and rectal screening swabs (4 patients). Epidemiological and whole genome sequencing data suggested a long-term carrier as the most likely source. Despite two rounds of mass suppression therapy of staff, using chlorhexidine initially, then octenidine-based regimens, positive patients continued to be identified. Staff screening subsequently identified one healthcare worker colonised with the outbreak strain of PVL-MSSA who underwent enhanced screening and further suppression therapy. No further cases have been identified to date. Compliance with mass suppression therapy was >95% and a post administration staff satisfaction survey showed the majority of staff agreed with the steps taken with low rates of adverse reactions.

CONCLUSION

Staphylococcus aureus outbreaks are commonly associated with colonisation of healthcare workers and are challenging to manage within environments such as neonatal units. Our study highlights the utility of whole genome sequencing in identifying and mapping an outbreak. We recommend that targeted staff screening should be considered early in similar outbreaks. In our setting mass suppression therapy was not an effective strategy despite a high level of staff engagement and compliance.

Neonatal Staphylococcus aureus acquisition at a tertiary intensive care unit

BACKGROUND

In this study, we explored the role of colonization in health care workers (HCWs) in transmission of methicillin-susceptible Staphylococcus aureus (MSSA) to neonates at a level IV neonatal intensive care unit (NICU).

METHODS

All available screening and clinical MSSA isolates, from the period March 2015 through April 2016, isolated from HCWs and neonates at the level IV NICU, were included. MSSA isolates were initially genotyped using spa typing, and for the most prevalent spa types, whole-genome sequencing (WGS) was performed.

RESULTS

From March 2015 through April 2016, 159 neonates and 115 HCWs were found positive for MSSA, and all isolates were typed by means of spa typing. Twenty-three spa types were found in both HCWs and neonates. Within the most prevalent spa types (t002, t015 and t2787), 4 WGS clusters of genetically indistinguishable MSSA isolates were found in which 4 HCWs and 35 neonates were involved. A total of 10 neonates included in the 4 WGS clusters suffered from bacteremia.

CONCLUSIONS

We showed that HCWs carried the same MSSA isolates as those found in neonates, and that HCWs might serve as a reservoir for transmission of MSSA to neonates. Ten neonates suffered from a bacteremia caused by a MSSA previously detected in a HCW.