Discussion

GAS outbreaks in hospitals, residential care facilities, and outpatient facilities are well documented, and guidelines exist for their investigation and management^[9,15,17,18]. However, despite a rising trend in HHC provision in Europe and the United States, the only published reports of HHC-associated iGAS outbreaks have come from England^[16].

HHC-associated infections are common. Data from the United States suggest that 3.2% of HHC patients become infected and require hospitalization or emergency care treatment and that wound infections are among the most common^[13]. The home environment poses infection control challenges that differ from acute healthcare settings, including limited ability to decontaminate hands, equipment, and the environment, and a lower quality of environmental cleaning. In addition, family members who sometimes help nursing staff do not have adequate training in infection control. A recent study from Belgium highlighted the need for better data on HHC-associated infections and for developing infection control guidelines specific to this setting^[19].

In England, the first HHC-associated iGAS outbreak was identified in 2013, and outbreak detection has been rapidly rising since then^[17]. Although all iGAS cases were notifiable in England during 2013–2021, characterization of isolates by the national reference laboratory is typically the trigger point for investigating clusters and no changes in isolate referral requirements were made during this period. However, local HPTs might have increasingly sought information on HHC after receiving advice from national teams, increased awareness, or both.

HHC services are under growing pressure because of a 46% reduction in qualified district nurses since 2010 and rising demand from an aging population with increasingly complex care needs. Nonspecialist nurses and healthcare assistants frequently are employed to deliver HHC. Among district nurses responding to a Queen’s Nursing Institute survey, 48% reported deferring visits or delaying patient care daily, 75% had unfilled vacancies on their teams, and 90% worked unpaid overtime hours^[20]. A King’s Fund report cited staff concerns over the quality and safety of care and reported wound care was particularly likely to be deprioritized during busy periods^[21].

We noted substantial delays in outbreak identification; 1 outbreak in our study (outbreak 4) was only identified when sporadic case isolates were used as sequencing controls to investigate another outbreak. Although detection delays were polyfactorial, a major contributing factor was that most outbreaks were caused by the 2 most common emm types in England, emm1 and emm89, making it difficult to distinguish outbreaks from sporadic cases. Compounding this problem were long intervals, up to 7 months, between sequential cases and no standardized method for HPTs to record and review emm types. Although HPTs were mandated by national guidelines to inquire about previous hospitalization and residential care, they did not routinely ask about HCC.

The value of WGS in investigating iGAS outbreaks is becoming increasingly recognized. In this study, the increased discrimination of WGS over emm typing confirmed that epidemiologically linked cases of common emm types formed genomic clusters. WGS also identified epidemiologically linked cases that did not form genomic clusters with outbreak cases, enabling exclusion of cases from investigation. WGS identification of genomic case clusters focused outbreak investigations and management, particularly where complex HHC-associated cases had multiple common exposures, such as residential care, wound management teams, and podiatry. Routine and timely WGS of all iGAS isolates could result in early and accurate identification of outbreaks.

WGS findings highlight the complexities of GAS transmission within the community, including cryptic carriage and infection or fomite transmission as the most credible connection between genomic case clusters in patients with distant epidemiologic links. In this study, HHCW screening by throat swab with bacterial culture in 9 outbreaks identified only 1 GAS carrier. Possible reasons for this low detection rate include delays in instigating screening because of lack of occupational health support and resistance from HHCW, which might mean that GAS infection or carriage resolved before screening. In addition, some HHCWs swabbed themselves or their colleagues, which might have introduced bias resulting from concerns about attributing blame. Finally, most HHCWs were screened by throat swab alone, and multiple published outbreaks have shown that HHCW GAS carriage from other sites can be responsible for transmission. Negative throat swab samples should not be used to exclude infection in a HHCW with an epidemiologic link to cases^[16,18].

GAS can persist on inanimate surfaces for up to 4 months and can contaminate fomites^[22,23], but the role of fomites in GAS transmission is difficult to establish. Previous published outbreaks were attributed to a diverse range of sources, including showerheads and bed curtains, but these objects were not definitively established as the only GAS source^[17,24]. Because fomite surface contamination can be transient and superficial contamination can be readily lost via subsequent contacts, failure to find GAS on any specific item does not exonerate the item from the transmission pathway. In this study, a single swab sample from a fabric bag handle tested positive for GAS, but insufficient data were available on number of swabs taken, and insufficient environmental swab samples were taken in other outbreaks, to establish whether fomites were a common transmission pathway. However, this positive sample highlights that equipment and hand contact surfaces can become contaminated. All HHCW equipment should be easy to decontaminate between patients’ homes, and single-use equipment should be available where possible.

The first limitation of this study is that data were collected retrospectively and might have been subject to recall bias. No recommended guidelines on investigation of HHCW outbreaks were available when this study was performed, and OCTs did not have standardized data collection methods, resulting in missing data in some outbreaks. HHCW teams were not interviewed as part of this study and their insight on outbreak management would have been useful.

In conclusion, HHC-associated iGAS outbreaks are now common and increasingly recognized in England and have high mortality rates. Further work is needed to elaborate GAS transmission dynamics within the HHC environment and guidelines are required to guide HPTs in the investigation and management of these outbreaks. Outbreak control is complex and can require multiple interventions, including improved infection control, equipment decontamination, and prophylactic antimicrobial drug therapy for staff. Nonetheless, public health agencies should be aware of HHC-associated iGAS. Although outbreaks can be difficult to identify among sporadic iGAS cases, prompt emm typing and WGS offer a means for timely recognition of case clusters.