Measuring social contacts in the emergency department

Abstract

Background: Infectious individuals in an emergency department (ED) bring substantial risks of cross infection. Data about the complex social and spatial structure of interpersonal contacts in the ED will aid construction of biologically plausible transmission risk models that can guide cross infection control.

Methods and findings: We sought to determine the number and duration of contacts among patients and staff in a large, busy ED. This prospective study was conducted between 1 July 2009 and 30 June 2010. Two 12-hour shifts per week were randomly selected for study. The study was conducted in the ED of an urban hospital. There were 81 shifts in the planned random sample of 104 (78%) with usable contact data, during which there were 9183 patient encounters. Of these, 6062 (66%) were approached to participate, of which 4732 (78%) agreed. Over the course of the year, 88 staff members participated (84%). A radiofrequency identification (RFID) system was installed and the ED divided into 89 distinct zones structured so copresence of two individuals in any zone implied a very high probability of contact <1 meter apart in space. During study observation periods, patients and staff were given RFID tags to wear. Contact events were recorded. These were further broken down with respect to the nature of the contacts, i.e., patient with patient, patient with staff, and staff with staff. 293,171 contact events were recorded, with a median of 22 contact events and 9 contacts with distinct individuals per participant per shift. Staff-staff interactions were more numerous and longer than patient-patient or patient-staff interactions.

Conclusions: We used RFID to quantify contacts between patients and staff in a busy ED. These results are useful for studies of the spread of infections. By understanding contact patterns most important in potential transmission, more effective prevention strategies may be implemented.

Figure 1. Floor plan of ED at EUHM. Red dots indicate RFID sensors. Zones are numbered and outlined in blue.

Figure 2. A schematic representation of contact, event, and duration.

The schematic above demonstrates how three individuals (A, B, and C) come into contact with each other over a 10-minute period.

Figure 3. Participation rate and percent of patients approached for each shift versus time, for the study year.

Figure 4. Distributions of the total minutes of contact between participants, by contact type.

Figure 5. Cumulative distributions of number of contacts per participant (degree) by contact type.