There have been four retrospective studies of the sales of diarrhea remedies during waterborne outbreaks of cryp-tosporidiosis (Proctor et al., 1998, Stirling et al., 2001, Edge et al., 2004, Rodman et al., 1997). All of these studies used similar sets of products (e.g., Kaopectate®, Imodium®, and Pepto Bismol®), and all found that sales of diarrhea remedies increased during outbreaks of cryptosporidiosis, and that the daily or weekly sales of diarrhea remedies rose and fell in proportion to the epidemic curve for the outbreak (although offset in time). Importantly, two studies found that significant increases in sales of diarrhea remedies preceded detection of the outbreak by the responsible public health organizations (Proctor et al., 1998, Stirling et al., 2001).
Proctor and colleagues studied sales of diarrhea remedies during the massive outbreak of cryptosporidiosis in Milwaukee in 1993 (Proctor et al., 1998). They obtained monthly counts of sales of diarrhea remedies from a single pharmacy in Milwaukee from March 1993—just prior to detection of the outbreak by health authorities—through July of 1995. They found that sales in March were approximately 600 units and sales in April were approximately 800 units. Monthly sales never exceeded 300 units in the ensuing two years after the outbreak. Given that the outbreak started in late March and public health became aware of the outbreak on April 5 (Mac Kenzie et al., 1994), even monthly sales data from a single pharmacy (for March 1993) may have provided four days earlier detection.
Stirling et al. (2001) studied sales of diarrhea remedies by three pharmacies during an outbreak of cryptosporidiosis in North Battleford, Saskatchewan. They found that weekly sales of diarrhea remedies increased seven-fold approximately three weeks prior to public health awareness of the outbreak and issuance of a drinking water advisory.
Edge et al. (2004) studied the relationship between sales of diarrhea remedies during the North Battleford outbreak (first studied by Stirling et al. ) and data about ED visits for gastrointestinal illness during the outbreak. They found that OTC sales data for this outbreak were a more sensitive and consistent indicator of disease activity than visits to the ED for gastrointestinal syndrome. They concluded that monitoring of sales of OTC diarrhea remedies is particularly important for diseases, such as cryptosporidiosis, that have relatively mild symptoms that individuals may self-treat rather than seek care at EDs or physician offices.
Rodman et al. (1997) attempted to synthesize information about sales of OTC diarrhea remedies for five waterborne outbreaks of cryptosporidiosis in the United States and Canada, including the Milwaukee outbreak. To our knowledge, this is the first study that attempted to analyze OTC sales data for multiple outbreaks. Unfortunately, they were only able to obtain sales of diarrhea remedies for one of the five outbreaks. During an outbreak of cryptosporidiosis that occurred in Collingwood, Ontario in 1996, one pharmacy in Collingwood saw a 26.4-fold increase in sales of diarrhea remedies during the first month of the outbreak relative to the same month in the previous year and 5.6 times higher in the second month. Their paper is also interesting because it summarizes interviews they conducted with pharmacists. During outbreaks that occurred in the cities of Kelowna and Cranbrook, in British Columbia, 10 to 12 pharmacies in each city related that sales of diarrhea remedies increased "significantly" during the outbreaks, but could not provide sales figures.
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