Food-borne illnesses during pregnancy

We wish to thank Dr Khatter and Ms Taylor and Dr Galanis for their interest in our Motherisk Update ‘Foodborne illnesses in pregnancy” in CFP in April 2010.

We believe that some of their recommendations are not evidence-based. We concur that it is important for pregnant women to be very careful in regards to consuming foods. However, despite their impressions, we did not make contradictory statements, as will be clearly shown here.

Despite the increased relative risk for pregnant women contracting Listeria, the absolute risk is extremely low and avoiding deli meats altogether does appear to be rather punitive. A risk assessment of Listeria monocytogenes in ready-to-eat foods conducted by the FDA/Center for Food Safety and Applied Nutrition and USDA/Food Safety and Inspection Service estimated the risk of developing listeriosis to be 1.2 x 10-5 (95% CI: 3.2 x 10-6 to 1.4 x 10-5) and 2.0 x 10-7 (95% CI: 4.8 x 10-11 to 5.3 x 10-6) per serving of deli meat and soft cheese, respectively, in the perinatal population. Taking the reciprocal of these values, the model estimates one case of listeriosis in 83000 servings of deli meat or 5 million servings of soft cheese consumed by a pregnant woman, which is a minimal risk (1).

To put this in perspective, for a woman who is less than 20 weeks of gestation, a conservative estimate of the risk of fetal loss following contact with an individual in the contagious stage of fifth disease (parvovirus B19 infection) is 1.8 x 10-3. This calculation uses the lower estimates of the proportion of the population that is not immune (35%), chance of maternal infection (20% in a daycare/school setting), and rate of vertical transmission (17%), and an estimated 14.8% rate of spontaneous loss of fetuses affected by parvovirus B19 before 20 weeks of gestation. For a woman who acquires the infection after 20 weeks of gestation, the estimated risk of fetal loss is lower (2.7 x 10-4), but still one order of magnitude higher than the risk of developing listeriosis following consumption of a single serving of deli meat. However, most government agencies do not recommend that pregnant women should routinely be excluded from a workplace where an outbreak of fifth disease is occurring (2).

We strongly believe that women should be informed of the nature and magnitude of the risks associated with the consumption of deli meats and soft cheeses. The decision to consume or avoid these foods should be made by her, based on this information, thus allowing her to make an informed decision. Subsequently, if she chooses not to avoid them, she should be advised on how she can minimize her exposure (and thus, her risk). Factors that determine exposure include amount and frequency of consumption, duration of refrigerated storage before consumption, and temperature at which the food is stored. We acknowledge that L. monocytogenes – unlike most bacterial pathogens – is able to grow at refrigeration temperatures (i.e., 4°C). However, growth at 4° is slow and limiting the duration of storage will limit bacterial growth.3

Therefore, she should be advised to: (1) limit the amount and frequency of consumption; (2) limit the duration of storage by choosing the freshest foods (i.e., those dated as close to the manufacture/packaging date as possible) and consuming them in a timely manner; (3) ensure that foods are kept at the correct temperature (less than 4°C) at all times including transport from the retail outlet to the home.

References 1.http://www.fda.gov/Food/ScienceResearch/ResearchAreas/RiskAssessmentSafetyAssessment/ucm184072.htm) 2.(http://www.sogc.org/guidelines/public/119E-CPG-September2002.pdf; http://www.cdc.gov/ncidod/dvrd/revb/respiratory/B19&preg.htm; Gillespie SM, et al. JAMA. 1990 Apr 18;263(15):2061-5; ACOG Practice Bulletin #20) 3.(http://fsrio.nal.usda.gov/document_fsheet.php?product_id=156; http://fsrio.nal.usda.gov/document_fsheet.php?product_id=221

While we were happy to see the issue of food safety in pregnancy addressed in the April 2010 Motherisk Update, “Food-borne illness during pregnancy” (1), we have concerns over some of the information presented which contradicts public health messages on this topic.

The authors state that there is increased incidence of disease or severe outcomes for the woman or neonate. However they recommend that foods which may contain L. monocytogenes (deli meats, soft cheese), Salmonella (eggs) or various bacteria, viruses and parasites (raw fish) are safe for consumption if properly handled and stored and purchased from a reputable supplier. These statements appear to contradict each other and are not supported by the literature and public health recommendations (2,3,4,5).

The authors do not provide references for many of their statements or in certain instances use references that are out of date or not representative of Canada. Non-published literature (e.g., government documents, guidelines) and content experts have not been consulted to identify recent Canadian outbreaks and public health programs and messages related to this topic.

The authors suggest that improved standards and surveillance have reduced the prevalence of contaminated foods in grocery stores and that the frequency of outbreaks has decreased. It is not possible to say whether the prevalence of contaminated foods and frequency of outbreaks have decreased. Some literature suggests that the number of outbreaks and the incidence of Salmonella and Listeria are increasing (6,7). Outbreaks and food recalls (8) related to listeriosis and deli meats (9,10) or soft cheese (11,12) and salmonellosis and eggs (7,13) continue to occur.

Food stored in a refrigerator allows the growth of Listeria which prefers to multiply at these temperatures (14). Proper storage therefore increases the risk of listeriosis. Proper handling of food (e.g., washing hands) is recommended, however foods such as deli meats and cheeses may already be contaminated when purchased. The consumer does not typically take additional steps at home (e.g., cooking) to reduce potential pathogens in such foods. Although purchasing food from a reputable supplier with approved food safety plans is a good suggestion, even reputable suppliers can have problems due to the ubiquitous nature of these pathogens in a food processing environment (9,10). Additionally, it is not possible for a pregnant woman to identify foods which have been prepared or stored appropriately in restaurants and outside of the home (e.g., flash frozen sushi, refrigerated eggs).

Finally, the authors have made some unfounded recommendations. The Public Health Agency of Canada and most provincial/territorial and local public health authorities in Canada and in many other countries recommend the following (3,4,15,16):

• Pregnant women should avoid consuming unpasteurised milk and dairy products, soft cheese (both pasteurized and unpasteurized), deli meats and smoked fish due to the potential risk of listeriosis. Such foods can only be safely eaten if heated to 74°C (165°F).

• Pregnant women and the general population should avoid consuming raw and under-cooked eggs. They should store eggs in the refrigerator and wash their hands and utensils/surfaces after contact with raw eggs. The use of pasteurized egg products is recommended when a recipe calls for raw eggs.

• Pregnant women and the general population should be aware that consuming raw fish, shellfish or raw bivalves (e.g., oysters) increases the risk of Vibrio, norovirus and other foodborne infections.

Research has shown that health-care providers may not provide sufficient information about risks associated with food safety to pregnant women and that messages should be improved and targeted (2,17,18,19). There is on-going work in Canada to address this.

Motherisk is a valuable and credible source of information for pregnant women and their health care providers. However, as evidenced by this article and another published2 in the same issue of Canadian Family Physician, further work is needed to improve food safety knowledge among pregnant women and their health care providers.

Marsha Taylor, Epidemiologist, BC Centre for Disease Control

Dr. Eleni Galanis, Physician Epidemiologist, BC Centre for Disease Control

(1) Tam C, Erebara A, Einarson A. Food-borne illness during pregnancy. Canadian Family Physician. April 2010; 56:341-343

(2) Kirkham C, Berkowitz J. Listeriosis in pregnancy. Canadian Family Physician. April 2010; 56:158-166.

(3) Public Health Agency of Canada. Listeria Protecting Your Pregnancy. (accessed at: http://www.phac-aspc.gc.ca/alert- alerte/listeria/pp-pg-eng.php)

(4) Centers for Disease Control. Listeria and Pregnancy. (accessed at: http://www.cdc.gov/ncbddd/pregnancy_gateway/infections-listeria.html)

(5) Kirkham C, Harris S, Gyzybowski S. Evidence-Based Prenatal Care: Part 1-General Prenatal Care and Counseling Issues. American Family Physician. 2005; 71(7).

(6) Lynch M, Painter J, Woodruff R, Braden C. Surveillance for Foodborne Disease Outbreaks-United States, 1998-2002. MMWR. November 2006; 55(SS10):1-34

(7) BCCDC Annual Report of Communicable Disease-2008. BC Centre for Disease Control (accessed at: http://www.bccdc.ca/NR/rdonlyres/59BFCFBB- 933D-4337-9305-E3E5FF30D272/0/EPI_Report_CDAnnual2008_20091202.pdf)

(8) Canadian Food Inspection Agency. Food Recall Alerts. (accessed at: http://www.inspection.gc.ca/english/corpaffr/recarapp/recaltoce.shtml)

(9) Attaran A, MacDonald N, Stanbrook MB, Sibbald B, Flegel K, Rajendra K, Hebert P. Listeriosis is the least of it. Canadian Medical Association Journal. October 2008. 179(8).

(10) Report of the Independent Investigator into the 2008 Listeriosis Outbreak. Government of Canada. July 2009

(11) Gaulin, C., Ramsay, D., Ringuette, L. and Ismaïl, J. First documented outbreak of Listeria monocytogenes in Quebec, 2002. Canadian Communicable Disease Report. 2003;29: 181-186.

(12) Clark, C. G., Farber, J., Pagotto, F., Ciampa, N., Doré, K., Nadon, C., Bernard,K., Ng, L.-K. and the CPHLN. Surveillance for Listeria monocytogenes and listeriosis, 1995-2004. Epidemiology and Infection, 2009;12: 1-14.

(13) Christopher R. Braden. Salmonella enterica Serotype Enteritidis and Eggs: A National Epidemic in the United States. Clinical Infectious Diseases 2006;43:512–7

(14) Rocourt J, Cossart P. Listeria monocytogenes In: Doyle MP, Beuchart LR, Montville TJ (eds.). Food Microbiology: Fundamentals and Frontiers. Washington, DC: ASM Press. 1997. 337-352.

(15) Health Canada. It’s Your Health-Listeria and Food Safety. (accessed at: http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/listeria- eng.php)

(16) Canadian Food Inspection Agency. Food Safety Facts on Listeria. (accessed at: http://www.inspection.gc.ca/english/fssa/concen/cause/listeriae.shtml)

(17) Bondarianzadeh D, Yeatman H, Condon-Paoloni D. Listeria education in pregnancy: lost opportunity for health professionals. Australia and New Zealand Journal of Public Health. 2007; 31(5):468-74.

(18) Cates SC, Carter-Young HL, Conley S, O’Brien B. Pregnant Women and Listeriosis: Preferred Educational Messages and Delivery Mechanisms. Journal of Nutrition Education Behaviour. 2004; 36:121-27

(19) Morales S, Kendall PA, Medeiros LC, Hillers V, Schroeder M. Health Care Providers’ Attitudes Toward Current Food Safety Recommendations for Pregnant Women. Applied Nursing Research. 2004;17(3):178-186