Foodborne illness outbreaks linked to unpasteurised milk and relationship to changes in state laws - United States, 1998-2018

Abstract

Consumption of unpasteurised milk in the United States has presented a public health challenge for decades because of the increased risk of pathogen transmission causing illness outbreaks. We analysed Foodborne Disease Outbreak Surveillance System data to characterise unpasteurised milk outbreaks. Using Poisson and negative binomial regression, we compared the number of outbreaks and outbreak-associated illnesses between jurisdictions grouped by legal status of unpasteurised milk sale based on a May 2019 survey of state laws. During 2013-2018, 75 outbreaks with 675 illnesses occurred that were linked to unpasteurised milk; of these, 325 illnesses (48%) were among people aged 0-19 years. Of 74 single-state outbreaks, 58 (78%) occurred in states where the sale of unpasteurised milk was expressly allowed. Compared with jurisdictions where retail sales were prohibited (n = 24), those where sales were expressly allowed (n = 27) were estimated to have 3.2 (95% CI 1.4-7.6) times greater number of outbreaks; of these, jurisdictions where sale was allowed in retail stores (n = 14) had 3.6 (95% CI 1.3-9.6) times greater number of outbreaks compared with those where sale was allowed on-farm only (n = 13). This study supports findings of previously published reports indicating that state laws resulting in increased availability of unpasteurised milk are associated with more outbreak-associated illnesses and outbreaks.

Keywords: foodborne illness; outbreak; public health; unpasteurised milk.

Fig. 1.

Bayesian negative binomial model (blue line) fit using a penalised thin plate spline to number of outbreak-associated illnesses (black line; top panel) and number of outbreaks (black line; bottom panel) linked to unpasteurised milk per year with 50% (dark blue), 90% (lighter blue), and 95% (lightest blue) credible intervals – FDOSS, United States, 1998–2018. This trend analysis was performed using R 4.0.0 and bamlss 1.1–2 with default settings [20]. Orange vertical lines demonstrate the 7-year time intervals compared by mean number of outbreaks and mean number of outbreak-associated illnesses.

Fig. 2.

Unpasteurised milk-associated outbreaks, by year and enteric pathogen – FDOSS, United States, 1998–2018.

Fig. 3.

Laws related to the sale of unpasteurised milk as of May 2019 and changes to laws 2012–2018 – United States. Provisions reviewed to generate this map are referenced in Table 4.