Outbreaks of FREE

MMWR. 1999;48:285-289

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In August 1998, the Minnesota Department of Health reported to CDC two restaurant-associated outbreaks of Shigella sonnei infections. Isolates from both outbreaks had two closely related pulsed-field gel electrophoresis (PFGE) patterns that differed only by a single band. Epidemiologic investigations implicated chopped, uncooked, curly parsley as the common vehicle for these outbreaks. Through inquiries to health departments and public health laboratories, six similar outbreaks were identified during July-August (in California [two], Massachusetts, and Florida in the United States and in Ontario and Alberta in Canada). Isolates from five of these outbreaks had the same PFGE pattern identified in the two outbreaks in Minnesota. This report describes the epidemiologic, traceback, environmental, and laboratory investigations, which implicated parsley imported from a farm in Mexico as the source of these outbreaks.

On August 17, the Minnesota Department of Health received reports of shigellosis in two persons who ate at the same restaurant during July 24-August 17. S. sonnei subsequently was isolated from stool samples of 43 ill restaurant patrons; an additional 167 persons had probable shigellosis (diarrhea [three or more loose stools during a 24-hour period] lasting ≥3 days or accompanied by fever). Eight (18%) of 44 restaurant employees had a similar illness; five had laboratory-confirmed S. sonnei infection. In a case-control study of 172 ill and 95 well restaurant patrons, five items were associated with illness: water (odds ratio [OR]=1.9; 95% confidence interval [CI]=1.0-3.8), ice (OR=3.7; 95% CI=1.6-8.6), potatoes (OR=2.6; 95% CI=1.5-4.6), uncooked parsley (OR=4.3; 95% CI=2.4-8.0), and raw tomato (OR=1.9; 95% CI=1.0-3.9). In a multivariate analysis, only uncooked parsley (OR=4.3; p<0.01) and ice (OR=6.9; p<0.01) remained significantly associated with illness.

On August 5, the Los Angeles County Department of Health Services was notified of two persons with shigellosis who ate at the same restaurant on July 31. Stool samples from six ill restaurant patrons yielded S. sonnei; an additional three had probable shigellosis (diarrhea [three or more loose stools during a 24-hour period], or any loose stools accompanied by fever). All 27 foodhandlers denied illness and had stool samples that were negative for S. sonnei. In an unmatched comparison with 10 well dining companions, ill patrons were significantly more likely to have eaten foods sprinkled with chopped, uncooked parsley (OR=32.0; 95% CI=1.8-1381.4).

On August 11, the Massachusetts Department of Health was notified of six persons who reported illness after eating at a restaurant lunch party on July 30. Stool samples from three persons yielded S. sonnei; an additional three had probable shigellosis (diarrhea within 4 days of the July 30 meal). Chopped, uncooked parsley was served on chicken sandwiches and in cole slaw served at the lunch. In a cohort study of 23 lunch attendees, illness was significantly associated with eating chicken sandwiches (relative risk [RR]=10.0; 95% CI=2.7-37.2) or eating uncooked parsley with any item (RR=10.0; 95% CI=1.4-70.2). All restaurant employees except one submitted a stool sample for culture; all were negative for S. sonnei.

On August 10, the Ontario Ministry of Health was notified of a family of three persons with S. sonnei infection who attended a food fair during July 31-August 3. Laboratory-based surveillance identified 32 additional persons with S. sonnei infection who had eaten at a specific kiosk at the fair or at the restaurant that had supplied the kiosk. Of the 35 persons, 20 were questioned about food history; all reported eating a smoked salmon and pasta dish made with fresh chopped parsley. Stool samples from six (38%) of 16 foodhandlers, including the four who handled the parsley, were negative for S. sonnei. One child who had eaten at the kiosk was the index patient at a day care center, from which five secondary cases of shigellosis were reported.

In addition to these four outbreaks, four additional restaurant-associated outbreaks of S. sonnei were identified, involving an additional 218 persons with culture-confirmed or probable shigellosis. Of the 111 persons interviewed, 106 (96%) reported eating chopped, uncooked, curly parsley. Isolates from three of these outbreaks (in Minnesota and California in the United States and in Alberta in Canada) matched the outbreak PFGE pattern. In the fourth outbreak (in Florida), one culture-confirmed case was identified; the isolate was not available for PFGE testing.

To determine the source(s) of parsley for the seven outbreaks linked by PFGE, state and provincial health departments, CDC, the Food and Drug Administration (FDA), and the Canadian Food Inspection Agency conducted traceback investigations. Farm A in Baja California, Mexico, was a possible source of parsley served in six of the seven outbreaks; four farms in California were possible sources of parsley in two to four of the seven outbreaks.

Field investigations of farm A by FDA and CDC found that the municipal water that supplied the packing shed was unchlorinated and vulnerable to contamination. This water was used for chilling the parsley in a hydrocooler immediately after harvest and for making ice with which the parsley was packaged for transport. Because the water in the hydrocooler was recirculated, bacterial contaminants in the water supply or on the parsley could have survived in the absence of chlorine and contaminated many boxes of parsley. Farm workers and village residents served by this water system reported drinking bottled water or water from other sources. Workers had limited hygiene education and limited sanitary facilities available on the farm at the time of the outbreak.

Foodhandlers at six (75%) of the eight implicated restaurants reported washing parsley before chopping it. Usually parsley was chopped in the morning and left at room temperature, sometimes until the end of the day, before it was served to customers.

The Minnesota Department of Health laboratory, which has tested isolates of S. sonnei by PFGE routinely since 1995, identified a previously unrecognized PFGE pattern of S. sonnei and a closely related pattern that differed by a single band associated with the two outbreaks in Minnesota. The pattern was distributed to other laboratories through PulseNet, the national molecular subtyping network for foodborne disease. In Minnesota and at CDC, strains from all seven outbreaks for which isolates were available for PFGE testing had the outbreak PFGE pattern. Isolates from the seven outbreaks were resistant to ampicillin, trimethoprim-sulfamethoxazole, tetracycline, sulfisoxazole, and streptomycin.

Investigators at the University of Georgia Center for Food Safety and Quality Enhancement conducted studies to determine the effects of temperature and handling on the growth and survival of S. sonnei on parsley. Colony-forming units of S. sonnei per gram (cfu/g) decreased by approximately 1 log per week on parsley, whether chopped or whole, under refrigeration (39 F [4 C]). In contrast, S. sonnei counts increased on parsley kept at room temperature (70 F [21 C]). On whole parsley, the increase was limited to 1 log cfu/g during the first 1-2 days, but on chopped parsley a 3 log cfu/g increase was observed within 24 hours.

L Crowe, W Lau, L McLeod, Calgary Regional Health Authority; CM Anand, Provincial Laboratory of Southern Alberta; B Ciebin, C LeBer, Ontario Ministry of Health; S McCartney, Ottawa-Carleton Health Unit; R Easy, C Clark, F Rodgers, National Enterics Laboratory, Health Canada; A Ellis, Health Canada; A Thomas, L Shields, B Tate, A Klappholz, I LaBerge, Canadian Food Inspection Agency. Reporter, H Sato, E Lehnkering, L Mascola, Los Angeles County Dept of Health Svcs, Los Angeles; J Waddell, S Waterman, State Epidemiologist, California Dept of Health Svcs. J Suarez, Miami-Dade County Health Dept, Miami; R Hammond, R Hopkins, State Epidemiologist, Florida Dept of Health. P Neves, Massachusetts Div of Food and Drugs; MS Horine, P Kludt, A DeMaria, Jr, State Epidemiologist, Massachusetts Dept of Public Health. C Hedberg, J Wicklund, J Besser, D Boxrud, B Hubner, M Osterholm, State Epidemiologist, Minnesota Dept of Health. FM Wu, L Beuchat, Center for Food Safety and Quality Enhancement, Univ of Georgia, Athens, Georgia. Food and Drug Administration. Epidemiology Br, Div of Parasitic Diseases; Hospital Environment Laboratory Br, Hospital Infections Program; Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; and EIS officers, CDC.

S. sonnei is a common cause of gastroenteritis, accounting for 10,262 ( 73%) of the 14,071 laboratory-confirmed Shigella infections reported to CDC in 1996.¹ Humans and other primates are the only reservoirs for S. sonnei, and transmission occurs through the fecal-oral route. As few as 10-100 organisms can cause infection, enabling person-to-person transmission where hygienic conditions are compromised. In the United States, S. sonnei primarily infects young children and is a common cause of diarrheal outbreaks in child care centers.² Although reported infrequently, foodborne outbreaks of shigellosis have been associated with raw produce, including green onions,³ iceberg lettuce,^4-7 and uncooked baby maize.⁸

Before the outbreak described in this report, PFGE was not used routinely by most state public health laboratories to subtype isolates of S. sonnei, making it difficult to detect clusters or outbreaks. This investigation demonstrated how the routine use of PFGE and PulseNet can link clusters of S. sonnei infections in widely dispersed geographic areas. This same technology is now used widely for comparing isolates of Escherichia coli O157:H7. CDC, in consultation with the Minnesota Department of Health, is developing a standard protocol for PFGE subtyping of S. sonnei isolates by PulseNet laboratories.

In the outbreak described in this report, isolates were resistant to many antimicrobial agents, including ampicillin and trimethoprim-sulfamethoxazole, which are commonly used to treat shigellosis. This highly resistant pattern is seen more frequently in countries other than the United States. During 1985-1995, antimicrobial resistance among Shigella increased substantially in the United States⁹: resistance to ampicillin increased from 32% to 67%, resistance to trimethoprim-sulfamethoxazole increased from 7% to 35%, and resistance to both agents increased from 6% to 19%. A history of international travel was the strongest risk factor for Shigella infection resistant to trimethoprim-sulfamethoxazole.⁹

The findings in this report indicate that several changes in food storage and food preparation procedures are needed. In restaurants, foodhandling practices such as pooling large batches of parsley for chopping and holding chopped parsley at room temperature increase the risk that sporadic low-level bacterial contamination will lead to outbreaks of gastrointestinal illness. When fresh produce is chopped, the release of nutrients may provide a favorable medium for bacterial growth. The risk for outbreaks can be reduced by storing chopped parsley for shorter times, keeping it refrigerated, and chopping smaller batches.¹⁰ Changes in parsley production on the farm (e.g., the use of adequately chlorinated water for chilling and icing parsley, education of farm workers on proper hygiene, and possibly the use of post-harvest control measures such as irradiation) may be necessary to ensure that produce is not contaminated with pathogens.

References: 10 available

MMWR. 1999;48:265-269

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During September 29, 1998-April 4, 1999, 229 cases of febrile encephalitis (111 [48%] fatal) were reported to the Malaysian Ministry of Health (MOH). During March 13-19, 1999, nine cases of similar encephalitic illnesses (one fatal) and two cases of respiratory illness occurred among abattoir workers in Singapore. Tissue culture isolation identified a previously unknown infectious agent from ill patients. This report summarizes the preliminary epidemiologic and laboratory investigations of these cases, which indicate that a previously unrecognized paramyxovirus related to, but distinct from, the Australian Hendra virus is associated with this outbreak.

A case of suspected illness was defined as fever, severe headache, myalgia, and signs of encephalitis or meningitis. Three clusters of cases have been identified. The first cluster began in late September 1998 near the city of Ipoh in the state of Perak. Cases continued to occur in this region until early February 1999. The second cluster occurred near the city of Sikamat in the state of Negri Sembilan in December 1998 and January 1999. The third and largest cluster began near the city of Bukit Pelandok in the state of Negri Sembilan in December 1998. Two cases occurred in the state of Selangor.

Cases have occurred primarily among adult men who had histories of close contact with swine. Concurrent with the human cases, illness and death occurred among swine from the same regions. Initially, Japanese encephalitis (JE) virus was considered the probable etiologic agent for this outbreak, and specimens from some patients tested positive for infection with JE virus. However, the predominance of cases in men who had close contact with swine suggested the possibility of another agent.

Tissue culture isolation from central nervous system specimens at the Department of Medical Microbiology, University of Malaya, identified a previously unknown infectious agent. Additional laboratory analysis at CDC of samples from 13 patients found recent JE virus infection in only one of 13 serum specimens. Electron microscopic studies of isolation material from three patients demonstrated virus-like structures consistent with a paramyxovirus, and immunofluorescence tests of cells infected with this virus suggested a virus related to Hendra virus (formerly called equine morbillivirus). Additional laboratory testing, including preliminary nucleotide sequence information, indicated the virus was related but not identical to the Hendra virus. Using a capture-IgM ELISA with prototype Hendra virus antigens, IgM antibodies were detected in the 12 JE-negative serum specimens. Tissues from three of four case-patients who died contained viral antigen that reacted with hyperimmune serum against Hendra virus by immunohistochemistry (IHC). All four specimens were negative for JE antigen.

Laboratory studies at CDC and in Malaysia demonstrated Hendra-virus IgM antibodies in serum specimens of 23 (88%) of 26 cases; in addition, Hendra-like antigens were detected in central nervous system tissue from four of five case-patients and from lung and kidney tissues of one case-patient tested. Hendra-like virus sequences have been found in four case-patients. Central nervous system, lung, and kidney tissues from swine from affected farms in Malaysia also have been positive for Hendra-like antigens by IHC.

Illness has been characterized by 3-14 days of fever and headache followed by drowsiness and disorientation that can progress to coma within 24-48 hours; a few patients had respiratory illness. Of the 229 case-patients, most have been men working on pig farms in Perak and Negri Sembilan. One case-patient became ill 10 days after his last known exposure to swine. Five cases have been reported in Malaysian abattoir workers exposed to swine. No cases have been reported among health-care workers caring for case-patients.

In some instances, illness in pigs occurred 1-2 weeks before illness in humans. The disease in swine is not well defined but appears to include rapid and labored breathing; an explosive nonproductive cough; and neurologic changes, including lethargy or aggressive behavior.

On March 7, 1999, a 49-year-old pig farmer in Malaysia developed fever, headache, behavior changes, and mild blurred vision. The following day, he became lethargic and was subsequently hospitalized with a diagnosis of viral fever. During the next several days, the farmer's neurologic status progressively worsened, and he developed generalized seizures, respiratory failure requiring mechanical ventilation, blood pressure instability, and high spiking fevers. He died on March 13.

On admission, complete blood count, electrolytes, and head computed tomography scan were normal. A lumbar puncture performed on March 13 showed no white blood cells, a normal glucose level, and a protein level of 2.09 g/L (normal: 0.15-0.45 g/L). The patient's serum was negative for JE virus IgM antibodies; his serum and cerebrospinal fluid (CSF) specimens were positive for Hendra-like virus IgM and IgG antibodies. A brother who had worked on the same pig farm and had died a few days earlier from encephalitis also had IgM antibodies to Hendra-like virus in both serum and CSF.

All 11 case-patients had handled swine imported from Malaysia. Serologic testing at CDC confirmed recent Hendra-like virus infection in these 11 workers, and limited nucleotide sequence studies of the virus from the patient who died suggest it is identical to that from the Malaysia outbreak. Antibodies to Hendra virus were detected at the Australian Animal Health Laboratories in blood samples from four of 100 pigs imported from Malaysia for slaughter in another Singapore abattoir.

In addition to active surveillance for encephalitis cases, studies are under way to determine risk, if any, for human-to-human transmission among health-care workers and family members, to confirm the source of human infection (presumedly pigs), to define specific risk factors associated with exposures to pigs and tissues from infected animals, and to determine the case-to-infection ratio and the epidemiology of this infection in pigs. Preliminary assessment suggests that spread of the virus among states in Malaysia has occurred through transport of infected swine. Susceptibility of other animal species is not known, and studies are under way to determine a presumed wildlife reservoir of this virus.

To prevent further outbreaks, Malaysian authorities have banned transport of pigs within the country. Army personnel and police are enforcing this ban, and quarantined pigs are being culled within a 3-mile (5-km) perimeter around recognized outbreak areas. In addition, Malaysian authorities recommend that all persons in the affected areas who have exposure to pigs (e.g., farm workers, truck drivers transporting animals, abattoir workers, and soldiers assisting in quarantine and culling of swine) use protective equipment, including protective clothing, gloves, boots, and masks.

Singapore and Thailand have banned importation of pigs from Malaysia. Singapore also has banned horses returning from Malaysia. The Malaysian MOH has initiated an education campaign to inform the public about the outbreak and about precautions during contact with pigs.

Dept of Medical Microbiology, Univ of Malaya, Kuala Lumpur; Institute for Medical Research; Vector Borne Disease Control Section, Disease Control Div, Ministry of Health; University Hospital, General Hospital, Kuala Lumpur; Seremban Hospital, Seremban; Ipoh Hospital, Ipoh; Institue of Veterinary Research, Veterinary Svc, Ministry of Agriculture; Ministry of Public Health, Malaysia. Changi General Hospital; Singapore General Hospital; Tan Tock Seng Hospital; Ministry of the Environment. Ministry of Health; Primary Production Dept, Ministry of National Development, Singapore. Commonwealth Scientific and Industrial Research Organization, Australian Animal Health Laboratory, Geelong, Queensland Dept of Primary Industries, Brisbane, Australia. Arbovirus Diseases Br, Div of Vectorborne Infectious Diseases; Div of Quarantine; Respiratory and Enteric Virus Br, Special Pathogens Br, Infectious Diseases Pathology Activity, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; and EIS officers, CDC.

Hendra virus was first recognized in September 1994 after an outbreak of respiratory illness among 20 horses and two humans in Hendra, Queensland, Australia¹; 13 horses and one human died. In 1995, a second unrelated outbreak was identified that had occurred in August 1994 in Mackay, Queensland, in which two horses died and one human became infected.^2,3 Transmissibility of Hendra virus from infected horses to other species appears to be low.⁴ All three previous human infections appear to have been acquired through exposure to blood or other body fluids or excretions of infected horses. Laboratory evidence suggests that fruit bats (Pteropus species) found in Australia⁵ and in Papua New Guinea may be the natural host for the virus. Despite close contact between fruit bats and bat researchers in Australia, serologic evidence of infection has not been found in these persons.⁶

The previously unrecognized paramyxovirus associated with these outbreaks of febrile encephalitis in Malaysia and Singapore is related to, but distinct from, the Australian Hendra virus.⁷ Serologic and IHC analyses support a causative role for this new virus in human and swine disease. Studies are under way to clarify what proportion of these illnesses is caused by infection with Hendra-like virus. The association between the disease in humans and pigs is supported by epidemiologic and laboratory data. Although the specific routes of transmission have yet to be determined, close contact with pigs appears to be necessary for human infection.

Travelers to Malaysia should be aware of these outbreaks of febrile encephalitis, which have involved only those closely associated with swine. No travel restrictions have been recommended or imposed at this time. U.S. residents anticipating travel to Malaysia should follow the CDC regional recommendations for Southeast Asia, which are available on the World-Wide Web at http://www.cdc.gov/travel/index.htm or http://www.cdc.gov/travel/seasia.htm. Persons in Malaysia are advised to contact the Malaysian health authorities for additional information. Information about the recent cases is available at the Malaysian Ministry of Health website at http://dph.gov.my.

References: 7 available