International outbreak of Salmonella Oranienburg due to German chocolate

Abstract

Background: This report describes a large international chocolate-associated Salmonella outbreak originating from Germany.

Methods: We conducted epidemiologic investigations including a case-control study, and food safety investigations. Salmonella (S.) Oranienburg isolates were subtyped by the use of pulsed-field gel electrophoresis (PFGE).

Results: From 1 October 2001 through 24 March 2002, an estimated excess of 439 S. Oranienburg notifications was registered in Germany. Simultaneously, an increase in S. Oranienburg infections was noted in other European countries in the Enter-net surveillance network. In a multistate matched case-control study in Germany, daily consumption of chocolate (matched odds ratio [MOR]: 4.8; 95% confidence interval [CI]: 1.3-26.5), having shopped at a large chain of discount grocery stores (MOR: 4.2; CI: 1.2-23.0), and consumption of chocolate purchased there (MOR: 5.0; CI: 1.1-47.0) were associated with illness. Subsequently, two brands from the same company, one exclusively produced for that chain, tested positive for S. Oranienburg. In two other European countries and in Canada chocolate from company A was ascertained that also contained S. Oranienburg. Isolates from humans and from chocolates had indistinguishable PFGE profiles. No source or point of contamination was identified. Epidemiological identification of chocolate as a vehicle of infections required two months, and was facilitated by proxy measures.

Conclusions: Despite the use of improved production technologies, the chocolate industry continues to carry a small risk of manufacturing Salmonella-containing products. Particularly in diffuse outbreak-settings, clear associations with surrogates of exposure should suffice to trigger public health action. Networks such as Enter-net have become invaluable for facilitating rapid and appropriate management of international outbreaks.

Figure 1

Disease onset (n = 362) of reported (n = 462) S. Oranienburg cases from reporting week 42/2001 to reporting week 12/2002 (outbreak period). The asterisk indicates the week when the (first) public warning was issued, and the incriminated chocolate products were recalled

Figure 2

Number of S. Oranienburg infections reported to the Enter-net database from participating countries, except Germany

Figure 3

Comparison of human S. Oranienburg isolates from the outbreak- period with strains of this serovar received sporadically before the outbreak by the use of PFGE (digested with XbaI, BlnI, and SpeI) lanes: 1–5: isolates from the outbreak period 6–13: isolates before the outbreak period S: molecular reference