Abstract
We outline a framework for evaluating food- and water-borne surveillance systems using hospitalization records, and demonstrate the approach using data on salmonellosis, campylobacteriosis and giardiasis in persons aged ≥65 years in Massachusetts. For each infection, and for each reporting jurisdiction, we generated smoothed standardized morbidity ratios (SMR) and surveillance to hospitalization ratios (SHR) by comparing observed surveillance counts with expected values or the number of hospitalized cases, respectively. We examined the spatial distribution of SHR and related this to the mean for the entire state. Through this approach municipalities that deviated from the typical experience were identified and suspected of under-reporting. Regression analysis revealed that SHR was a significant predictor of SMR, after adjusting for population age-structure. This confirms that the spatial “signal” depicted by surveillance is in part influenced by inconsistent testing and reporting practices since municipalities that reported fewer cases relative to the number of hospitalizations had a lower relative risk (as estimated by SMR). Periodic assessment of SHR has potential in assessing the performance of surveillance systems.
Highlights
Foodborne illness affects an estimated 47.8 million people in the United States each year, causing more than 128,000 hospitalizations and 3,000 deaths [1,2]
Using Massachusetts as a case study, we show that comparison of surveillance and hospitalization data could be a useful tool for identifying geographic areas that deviate from the typical experience and might be underascertaining cases of reportable disease
Notifiable disease counts and annual rate of disease by etiology and data source are shown in Table 1 along with the crude surveillance to hospitalization ratios (SHR) for each infection
Summary
Foodborne illness affects an estimated 47.8 million people in the United States each year, causing more than 128,000 hospitalizations and 3,000 deaths [1,2]. The total health-related cost of foodborne illness is likely to be as much as $77 billion per year [4], while hospitalization costs associated with three common waterborne pathogens alone cost the healthcare system an estimated $539 million annually [5]. In the United States, surveillance for notifiable diseases – including those transmitted via food and water – falls within the mandate of local and state governments. These surveillance systems typically rely on passive reporting by laboratories and healthcare providers who notify local health authorities when cases are diagnosed. National surveillance systems are expanding the number and range of proxies evaluated to better characterize the burden of infection and performance of public health surveillance [9,10]
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