In 2008, a pregnant female in her 30s presented to a British Col­um­bia hospital with a stiff neck, fever, back pain, and headache at 21 weeks’ gestation. She went into premature labor and delivered a stillborn baby the following day. Listeria mono­cytogenes was isolated from her blood and the placenta. 

This previously healthy woman had made changes to her diet which she felt would improve her baby’s health, including eating more dairy. Three weeks prior to her illness, she had consumed queso blanco (a fresh, soft cheese, often unpasteurized). In hospital, she learned that queso blanco is a food that pregnant women should avoid due to the risk of listeriosis associated with unpasteurized dairy products and soft cheeses. 

Although she had been counseled about food during her pregnancy, she was not aware of Listeria or its potential risk to her and her baby. This case highlights a gap in the awareness of high-risk foods and listeriosis and preventive actions that can be taken by pregnant women. The information provided to pregnant women by health care providers needs to be targeted and clear. 

Listeria monocytogenes is a bacterium transmitted by contact with infected animals through vertical transmission or by eating contaminated food (see the ). Listeria can be found in raw foods, such as meats and produce, as well as in processed refrigerated foods (e.g., soft cheeses and cold cuts). These processed products are a unique concern as, unlike most bacteria, Listeria can survive on refrigerated foods and tolerate humid and salty environments. 

Listeria are killed by pasteurization and cooking.[1] The incubation period ranges from 3 to 70 days, with a median of 3 weeks.[2] Symp­toms include fever, myalgias, headache, and diarrhea; serious cases of meningoencephalitis and sepsis can be fatal. The case fatality rate among nonpregnant adults is 20%.[3] 

Pregnant women, the elderly, and immunocompromised individuals are at increased risk of infection. In pregnant women, outcomes such as miscarriage, stillbirth, or illness in the newborn may occur.[2]

In BC between January 2002 and May 2008, 70 cases of listeriosis were reported; seven individuals (10%) were pregnant, four of whom (57%) had a miscarriage or stillbirth and six (86%) reported consumption of high risk foods, demonstrating a possible lack of awareness of listeriosis risks.

An American study concluded that pregnant women were unfamiliar with Listeria and few received information about food safety from their health care providers while pregnant.[11] In Aus­tralia, over 57% of pregnant women surveyed had an incomplete knowledge of high-risk foods and 25% continued to consume foods such as deli meats and paté.[12] These studies and others[13,14,15] identified that the information available on food safety and listeriosis during pregnancy was insufficient and better resources should be developed and incorporated into routine counseling by health care providers.
 
Similar gaps have been identified in food safety counseling by BC health care providers during pregnancy. Interviews were conducted with health care providers in BC, including public health nurses, obstetricians, midwives, and family physicians from March to May 2008 to learn about their awareness, practices, and needs. 

All of the health care providers were aware of listeriosis and provided information on food and nutrition to their patients during pregnancy; however, they did not all provide counseling on food safety or specific listeriosis risks. Health care providers felt that their limited or inconsistent knowledge of listeriosis risk factors was a significant barrier. 

Health care providers wanted better information for themselves and resources that they could share with pregnant women. Further work by BCCDC is planned to develop these resources. 

Pregnant women identify their health care providers as a credible source of information and rely on them to provide them with accurate advice. Health care providers should counsel their pregnant patients about the risks associated with listeriosis. 

Most cases of listeriosis in pregnancy could be prevented by avoiding consumption of certain foods and contact with certain animals, as well as proper food preparation (see the Figure [12]). On­going work in BC will lead to the development of improved materials to assist both health care providers and pregnant women in addressing food safety risks during pregnancy. 

For more information on listeriosis please visit: 
• www.bccdc.org/topic.php?item=108 [13]
• www.bchealthguide.org/healthfiles/hfile75.stm [14]
• www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/listeria-eng.php [15]

References

1. Food Directorate, Health Products and Food Branch, Health Canada. Policy on Listeria monocytogenes in Ready-to-Eat Foods. 2004. www.hc-sc.gc.ca/fn-an/legislation/pol/policy_listeria_monocytogenes_politique_toc-eng.php [16] (accessed 21 July 2008).
2. Heymann DL (ed.). Control of Communicable Diseases Manual. American Public Health Association; 2004:309-312.
3. Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United States. Emerg Infect Dis 1999;5:607-625.
4. Centers for Disease Control and Prevention (CDC).Outbreak of listeriosis associated with homemade Mexican-style cheese—North Carolina, October–January 2001. MMWR Morb Mortal Wkly Rep 2001; 50:560-562.
5. Lundén J, Tolvanen R, Korkeala H. Human listeriosis outbreaks linked to dairy products in Europe. J Dairy Sci 2004;87:(suppl):E6-E11.
6. Hayes PS, Feeley JC, Graves LM, et al. Isolation of Listeria monocytogenes  from raw milk. Appl Environ Microbiol 1986;51:438-440.
7. Centers for Disease Control and Prevention (CDC). Multistate outbreak of lis­teri­osis—United Sates, 1998. MMWR Morb Mortal Wkly Rep 1998;47:1085-1086.
8. Centers for Disease Control and Prevention (CDC). Multistate outbreak of listeriosis—United States, 2000. MMWR Morb Mortal Wkly Rep 2000;49:1129-1130.
9. McLauchlin J, Hall SM, Velani SK, et al. Human listeriosis and paté: A possible association. BMJ. 1991;303(6805):773-775.
10. Jørgensen LV, Huss HH. Prevalence and growth of Listeria monocytogenes in naturally contaminated seafood. Int J Food Microbiol 1998;42:127-131.
11. Cates SC, Carter-Young HL, Conley S, et al. Pregnant women and listeriosis: Preferred educational messages and delivery mechanisms. J Nutr Educ Behav. 2004;36:121-127.
12. Bondarlanzadeh D, Yeatman, H, Condon-Paoloni D. Listeria education in preg­nancy: Lost opportunity for health professionals. Aust N Z J Public Health. 2007;31:468-474.
13. Ogunmodede F, Jones JL, Scheftel J, et al. Listeriosis prevention knowledge among pregnant women in the USA. Infect Dis Obstet Gynecol 2005;13:11-15.
14. Torvaldsen S, Kurinczuk JJ, Bower C, et al. Listeria awareness among new mothers in western Australia. Aust N Z J Public Health 1999;23:362-367.
15. Morales S, Kendall PA, Medeiros LC, et al. Health care providers’ attitudes toward current food safety recommendations for pregnant women. Appl Nurs Res 2004;17:178-186.

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Ms Taylor is a field epidemiologist with Epidemiology Services, BC Centre for Disease Control and the Canadian Field Epidemiology Program, Public Health Agency of Canada. Ms Bitzikos is an environmental health officer with Vancouver Coastal Health Authority. Dr Galanis is a physician epidemiologist with Epidemiology Services, BC Centre for Disease Control.