Since May 1993, three cases of infection with Salmonella serotype Tennessee in infants in Canada and the United States have been linked to consumption of contaminated powdered infant formula. This report summarizes preliminary data on isolation of this organism from powdered milk products and alerts laboratories to the poss ibility that, because this strain may ferment lactose, it may not be identified as Salmonella.

Following the isolation of Salmonella serotype Tennessee from the stools of two infants in Canada who had consumed Soyalac Powder(R) infant formula in May, the Food and Drug Administration (FDA) isolated Salmonella Tennessee from production equipment at the Minnesota plant where the product had been dried, and from cans of the powdered infant formula. In June 1993, one case of infection with Salmonella Tennessee occurred in Illinois in an infant who consumed Soyalac Powder(R). From November 4, 1992, through June 29, 1993, 48 cases of infection with Salmonella Tennessee have been reported to CDC; when annualized, this number is not substantially different from the mean of 120 cases reported annually from 1981 through 1991.

On June 28, 1993, FDA ordered a recall of all Soyalac Powder(R) infant formula produced on or after November 4, 1992. FDA has identified additional products that are spray-dried at this plant; these products include Sumacal(R) medical food supplement, Propac(R) protein supplement, canned Medibase(R) medical meal replacement, Kresto Denia(R) powdered milk, Enercal(R) diet beverage, Enercal Plus(R), and Promil(R) weaning formula. No cases of illness have been linked to these products. FDA is working with plant officials to determine whether any other products were dried or packaged at this plant during this time. No spray-dried products have been distributed from this plant since June 7, 1993. FDA has requested recall of all products spray-dried at this plant since November 4, 1992. More detailed product information is available from the Division of Emergency and Epidemiological Operations, FDA, telephone (301) 443-1240.

Reported by: KK Louie, REHO, Boundary Health Unit, Surrey, British Columbia; AM Paccagnella, WD Osei, British Columbia Center for Disease Control, Vancouver; H Lior, MSc, Chief, National Laboratory for Enteric Pathogens, Laboratory Center for Disease Control, Ottawa, Ontario, Canada. BJ Francis, MD, State Epidemiologist, Illinois Dept of Public Health. MT Osterholm, PhD, State Epidemiologist, Minnesota Dept of Health. Minneapolis District, Center for Food Safety and Applied Nutrition, Food and Drug Administration. Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Outbreaks of salmonellosis caused by powdered milk products have been reported in the United States (1) and elsewhere (2,3). The isolates of Salmonella Tennessee that were identified from the three infants described in this report are atypical of salmonellae because most colonies ferment lactose and, therefore, may not be detected by clinical laboratories that use media or methods that identify salmonellae based on absence of lactose fermentation.

To isolate this organism, plating media that include an indicator of hydrogen sulfide (H2S) production, such as bismuth sulfite (BS) agar, Hektoen enteric (HE) agar, or xylose-lysine-deoxycholate (XLD) agar, should be used. BS does not contain lactose, so typical H2S-producing (black) colonies can be selected from this medium. Both HE and XLD contain an indicator of H2S production, as well as lactose; selection of colonies from these media should be based on H2S production rather than absence of lactose fermentation. At CDC, H2S production by this strain was detected more easily on HE than on XLD. Use of either BS or HE is recommended for recovery of this strain. XLD agar should be used only if other media are not available.

To screen colonies selected from isolation plates, lysine-iron agar (LIA) is recommended because the reaction produced by lactose-fermenting salmonellae in this medium is typical and because H2S produced by lactose-fermenting organisms can be detected. Triple sugar iron agar (TSI) or other media that depend on lactose fermentation to identify suspect salmonellae should not be used. H2S production may not be detected on TSI because of acidic conditions caused by fermentation of lactose. Automated test systems should be used with caution, since lactose-fermenting salmonellae tested at CDC in several such systems were sometimes identified incorrectly. This particular strain was correctly identified as Salmonella by the Analytab Products' API 20E(R) * system.

CDC requests that health-care providers and public health departments continue routine reporting to the Salmonella surveillance system; that all Salmonella serogroup C1 (of which Salmonella Tennessee is a member) isolates be serotyped; that persons infected with Salmonella Tennessee be questioned specifically about consumption of powdered milk products or infant formula; and that, until August 15, 1993, new cases of infection with Salmonella Tennessee, whether lactose fermenting or nonlactose fermenting, be reported promptly to the state health department.

References

1. Collins RN, Treger MD, Goldsby JB, Boring JR III, Coohon DB, Barr RN. Interstate outbreak of Salmonella newbrunswick infection traced to powdered milk. JAMA 1968;203:838-44.

2. Weissman JB, Deen RMAD, Williams M, Swanston N, Ali S. An island-wide epidemic of salmonellosis in Trinidad traced to contaminated powdered milk. West Indian Med J 1977; 26:135-43.

3. Rowe B, Begg NT, Hutchinson DN, et al. Salmonella Ealing infections associated with consumption of infant dried milk. Lancet 1987;2:900-3.

• Use of trade names and commercial sources is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.

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