Session: Poster Session: Outbreaks
Sunday, October 26, 2008: 12:00 AM
Room: Hall C
Background: Outbreaks of invasive group A Streptococcus (GAS) often do not identify specific routes of transmission. We sought to understand GAS transmission patterns by investigating an outbreak in a long-term acute care facility that occurred from Oct 12 to Feb 18, 2008. Methods: We mapped room assignments of all cases (n=11) and roommates during the outbreak, and tracked direct staff contact with cases. A carriage study identified 2 GAS-colonized staff. We conducted a 4:1 case-control study during the peak outbreak period (January) to assess potential association between cases and colonized staff. We defined cases as patients with GAS culture-positive infections and controls as patients with no evidence of GAS infection. Direct care contact with cases and controls was analyzed for the 5 days prior to each case’s GAS culture dates. Results: Cases’ room assignments changed a median of 4 times (range 1-10) during the outbreak and twice (range 1-4) after GAS was cultured. A patient without GAS infection was placed in a known GAS + patient room on 4 occasions, once following recommendations to cohort similarly-ill patients and to use single occupancy rooms. Three incorrectly cohorted roommates became cases; the fourth was later identified as a carrier. Multiple infection control breaches (e.g., gloved use of in-room keyboards) were noted. One staff carrier was not more likely to care for cases vs. controls [OR=1.1 (95% C.I. 0.3-4.2)]; the other had no case contact during January. Conclusions: Frequent patient movement and improper cohorting likely contributed to disease propagation. Although the primary mechanism of transmission may have been general infection control breaches rather than direct transmission of GAS from a healthcare worker to patients, we could not rule out transmission by colonized staff. When possible, GAS-infected residents should be cohorted or placed in single-occupancy rooms.