Importance of "Super-spreaders" in Infectious Disease Outbreaks

Entering Honduras during the H1N1 influenza
pandemic, June 2009

Here is an interesting article from Slate looking at the role of "super-spreaders" in infectious disease outbreaks. This refers to a sub-population of individuals who are more likely to spread an infectious disease than others; it is believed such "super-spreaders" played a role in the SARS pandemic. Identifying these individuals may have a role in managing global infectious disease outbreaks.

At the hospital level, Polgreen and colleagues have studied this phenomenon as it applies to hand hygiene and disease spread. Their work supports the idea that certain healthcare workers are more likely to spread an infectious disease, and has implications for targeting these individuals to prevent disease spread (via such things as optimizing hand hygiene, et cetera).  

Impact of a Water Sanitation & Hygiene Program in Western Kenya

Latrine in La Hicaca, Honduras

This is an interesting study by Greene and colleagues that examined the impact of a school-based improved water, sanitation and hygiene (WASH) program in Western Kenya on fecal contamination of students’ hands with E. Coli. 17 intervention and 17 control schools were assessed (as a sample of a larger cluster randomized trial of 135 schools). Intervention schools had specialized buckets provided for hand washing and drinking water, as well as a supply of hypochlorite solution provided for water decontamination. Teachers were trained on how to maintain the handwashing equipment. Schools with a high ratio of students to latrines underwent the addition of new latrines to meet a pupil to latrine ratio of 30:1 for boys and 25:1 for girls.

These authors found no difference in E. coli hand contamination for the intervention and the control schools, and curiously found an increased risk of hand contamination for girls in schools where new latrines had been constructed (RR: 2.63, 95% CI 1.29-5.34). Although it is not clear why this occurred, the authors postulate that this increase in contamination may have occurred secondary to increased latrine use in the absence of improvements in hand hygiene. The authors note poor student access to soap, a fact that likely critically undermined the overall sanitation program. In a geographically discrete location such as a school, the introduction of latrines in the absence of mechanisms to improve hand hygiene may actually lead to increased fecal contamination of hands, with the potential for spread of diarrheal illness.

Although improving access to latrines is a critical component of improving the overall health of communities, improving latrine access without improving access to soap may actually be harmful. Mechanisms to assure soap access should be built in to hygiene programs.