Prolonged and large outbreak of invasive group A Streptococcus disease within a nursing home: repeated intrafacility transmission of a single strain

Abstract

Objectives: Multiple invasive group A Streptococcus (GAS) infections were reported to public health by a skilled nursing facility (facility A) in Illinois between May 2014 and August 2016. Cases continued despite interventions including antibiotic prophylaxis for all residents and staff. Two other geographically close facilities reported contemporaneous outbreaks of GAS. We investigated potential reasons for ongoing transmission.

Methods: We obtained epidemiologic data from chart review of cases and review of facility and public health records from previous investigations into the outbreak. Infection control practices at facility A were observed and evaluated. Whole genome sequencing followed by phylogenetic analysis was performed on available isolates from the three facilities.

Results: From 2014 to 2016, 19 invasive and 60 noninvasive GAS infections were identified at facility A occurring in three clusters. Infection control evaluations during clusters 2 and 3 identified hand hygiene compliance rates of 14% to 25%, appropriate personal protective equipment use in only 33% of observed instances, and deficient wound-care practices. GAS isolates from residents and staff of all three facilities were subtype emm89.0; on phylogenetic analysis, facility A isolates were monophyletic and distinct.

Conclusions: Inadequate infection control and improper wound-care practices likely led to this 28-month-long outbreak of severe infections in a skilled nursing facility. Whole genome sequencing and phylogenetic analysis suggested that intrafacility transmission of a single highly transmissible GAS strain was responsible for the outbreak in facility A. Integration of genomic epidemiology tools with traditional epidemiology and infection control assessments was helpful in investigation of a facility-wide outbreak.

Keywords: Group A; Intrafacility transmission; Invasive; Outbreak; Single strain; Streptococcal disease.

Fig. 1.

(a) Epidemic curve of cases of GAS infections among residents at facility A, May 2014 to August 2016. (b) Epidemic curve of cases of GAS infections among staff at facility A, May 2014 to August 2016. GAS, group A Streptococcus.

Fig. 2.

Phylogenetic tree comprising emm89.0 isolates from facility A and two-facility cluster at city B, along with other emm89.0 isolates from Illinois (community) and other ABCs sites: CA, California; CT, Connecticut; GA, Georgia; MN, Minnesota; NM, New Mexico; NY, New York; OR, Oregon; TN, Tennessee. Sample information is encoded within tip labels. Tip labels shaded blue correspond to facility A and those shaded pink correspond to city B. For samples from facility A, labels that begin with ‘C indicate GAS-colonized sample, while ‘S’ and ‘R’ designation represent staff and resident, respectively. Number after ‘S’ or ‘R’ is staff or resident index number. Cases where multiple samples were taken from individual at different time points are coded by letter after index number. When multiple samples were taken from same individual at same time point, numeric identifier is assigned following underscore. Isolates from city B facilities are labeled as city-B-X. Isolates from city A but not linked to facility A are labeled as city-A-X. Isolates from rest of Illinois are labeled as ILx and ABCs isolates as ABCx. GAS, group A Streptococcus.

Fig. 3.

Time-scaled phylogeny of 57 facility A isolates which formed monophyletic clade on phylogenetic tree, generated using methods detailed in Supplementary Materials. Scale axis represents number of days preceding 20 August 2016 sampling date of most recent outbreak isolate. Green vertical line indicates chemoprophylaxis treatment at end of April 2015. Clade highlighted in yellow suggests possible cluster of postchemoprophylaxis isolates. Clade branch highlighted in blue contains samples highly related to wound-care nurse CS18. Sample information is encoded within tip labels. Labels that begin with ‘C indicate GAS-colonized sample, while ‘S’ and ‘R’ designation represent staff and resident, respectively. Staff samples are also highlighted in red. Number after ‘S’ or ‘R’ is staff or resident index number. Cases where multiple samples were taken from same individual at different time points are coded by letter after index number. If multiple samples were taken from same individual at same time point, numeric identifier is assigned after underscore. GAS, group A Streptococcus.

Fig. 4.

Schematic illustrating how BaTS AI score was used to discern whether chemoprophylaxis treatment had significant impact on stopping spread of infection. (a) Chemoprophylaxis was ineffective. (b) Chemoprophylaxis was partially effective, with transmission continuing but limited to certain individuals. (c) Chemoprophylaxis effective but a separate strain was introduced. Blue and orange nodes indicate pre- and postchemoprophylaxis strains, respectively; chemoprophylaxis event is represented by green vertical line. Each time-measured phylogeny represents different postprophylaxis outcome. In all three cases, there are 14 postprophylaxis strains, but each tree differs by amount of postprophylaxis clustering. AI, association index.