Listeria 

A highly publicized national outbreak of Listeria monocytogenes has focused attention and raised awareness of this relatively uncommon but potentially serious foodborne infection. Physicians can reduce the morbidity and mortality of Listeria infections in several ways including: 1) Educating patients at high risk for illness about Listeriosis and precautions they can take to reduce their risk 2) Considering Listeria in the differential in appropriate individuals and promptly initiating therapy 3) Promptly notifying the WCDH of any cases of Listeriosis - this will result in an investigation and possible identification of contaminated a food source. Timely recalls of such foods can prevent others from becoming ill. 4) Having all clinical isolates of Listeria for molecular typing (DNA fingerprinting). The WCDH can facilitate or arrange this if notified. Molecular typing can identify outbreaks and food sources when there are relatively few cases which occur over longer periods of time and a wide geographical distribution. Two recent outbreaks which otherwise may have gone undetected were identified in this manner.

Outbreaks

Beginning August 1998, an outbreak involving 17 states, including New York has resulted in about 80 cases and 15 deaths. Five of the deaths have been miscarriages - fetuses or infants of pregnant women infected with Listeria. This outbreak has been linked to contaminated hot dogs and deli meats distributed by the Bil Mar Foods division of Sara Lee and a recall of these contaminated products dates to 22 December 1998. In February 1999, a second outbreak was identified involving 8 cases in 3 states, including New York (NY state cases are in NYC) ,and has been linked to Mragowski cheese which is frequently sold at Polish deli's.

Epidemiology

Although no cases of Listeria infections involved in these outbreaks have been identified in Westchester County, 3 of 6 cases of Listeriosis reported during 1998 occurred in pregnant women, and all 3 infections resulted in either pre-term delivery or miscarriage. An average of 4-6 Listeria infections a year are reported annually to the Westchester County Health Department. Prior to 1998, most of the cases occurred in elderly individuals with underlying health problems.

Listeria monocytogenes infections, although much less common (1-2,000 cases/yr in the U.S.), is more serious than other foodborne illnesses, with 25% of cases being fatal. It is thus not a common cause of illness in the general population but can cause life threatening meningoencephalitis and bacteremia in neonates, pregnant women, immunosuppressed individuals, and the elderly. Education regarding Listeria is particularly beneficial to such individuals. Knowledge and awareness of Listeria infections among the general public appears to be much lower than that for other foodborne illnesses, such E.coli 0157:H7.  These high-risk individuals are also advised to be alerted to recalls of foods contaminated with Listeria such as those described in more detail below.

Listeria is widespread in nature and found commonly in soil, decaying vegetation, and in the fecal flora of many mammals. Listeria has also been recovered from many foods including unpasteurized dairy products, raw vegetables, meats, poultry, and fish. Although there are at least 16 serotypes of Listeria monocytogenes, almost all disease is due to types 4b (the recent outbreaks), 1/2a, and 1/2b.

Precautions Against Listeria Infections

The general public, but particularly pregnant women and others at increased risk, are advised to take the following precautions against acquiring Listeria infections:

• Avoiding high risk foods such as soft or runny cheeses such as feta, Brie, Camembert, and Mexican style cheese
• Avoiding or thoroughly cooking until steaming hot: hot dogs, cold cuts, or leftovers
• Thoroughly cooking all raw food from animal sources, such as beef, pork, or poultry
• Always washing raw vegetables before eating
• Never consuming raw (unpasteurized) dairy products - dairy products eaten or from abroad may not be routinely pasteurized
• Keeping uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods
• Washing hands, knives, and cutting boards thoroughly after handling uncooked foods

Clinical Information

Listeria infection may not cause any illness in most individuals or only cause a mild self-limited flu-like illness in pregnant women and frequently be unrecognized. If left untreated during pregnancy, it can lead to premature delivery and fetal death. About 20% of Listeria infections occur in pregnant women and most occur during the third trimester. Meningitis and bacteremia are the most commonly recognized clinical syndromes; it is the fourth most common cause of meningitis in the U.S., one of three major causes of neonatal meningitis, and the leading cause of meningitis in individuals receiving corticosteroids, lymphomas, and organ transplant recipients. Nuchal rigidity is less common (15-20%) but movement disorders, seizures, and fluctuating mental status are more common (20-25%) than with other bacterial meningitides. On exam of CSF, Gram stain is negative and glucose in normal in over half of cases and there is a predominance of mononuclear cells in about one third of cases.

Listeria infection should thus be considered in the differential of high-risk patients presenting with compatible clinical findings. A history of eating any high-risk food items is helpful. High-risk foods include soft cheeses (which are at increased risk of contamination even following pasteurization), particularly those eaten abroad, or undercooked hot dogs.

Diagnosis is established by positive blood cultures, or lumbar puncture and CSF cultures.

Treatment - The recommended treatment for Listeriosis is ampicillin (1.5 - 2.0 gm q 4-6 hrs) and gentamicin (5 mg/kg q 8 hrs) for 2 weeks (if bacteremia only) or 3 weeks (if CNS infection is present). Penicillin, in high doses (3 million units q 4 hrs), or TMP/SMX (20 mg/kg/day) divided into 4 doses, or erythromycin (1 gm q 6 hrs) are alternative regimens which have been used with successful outcomes, although clinical experience with these latter is limited. Gentamicin is generally contraindicated during pregnancy.

Food Recalls

In response to the outbreak linked to hot dogs and deli meats distributed by Sara Lee, there has been an increased number of foods tested for and found to contain Listeria. Because serotyping testing is not readily available and the infectious inoculum for Listeria is not established, the significance of these findings is not entirely clear but many food manufacturers have recalled their products. Some of the more widely distributed and well known products that have been recalled since January 1999 include Oscar Meyer variety lunchmeats and Thorn Apple Valley hot dogs and lunch meats. Except for the Sara Lee and Mragowski cheese outbreaks described above, NO human illnesses have been identified in association with these products. Individuals at high risk for infection with Listeria can reduce their risk for illness by being alerted to these recalls, on which detailed information is available through the Westchester County Department of Health website or by calling the Westchester County Department of Health. Recalled items should be returned to the store of purchase for a refund.

References:   MMWR, 47(51 & 52):1117-8. 8 Jan 1999
                    Clin. Inf. Dis. 24:1-11. 1997.

For further information about Listeria infections or recalled products, or to obtain a copy of a patient information sheet, contact Dr. Ada Huang at the Westchester County Department of Health at 637-4910 or visit our website at www.co.westchester.ny.us/health.

Harold N. Adel, M.D., M.P.H.., Commissioner
Ada Huang, M.D., Deputy Commissioner, Disease Control

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