Daniel N. Cameron

Clinical, epidemiological, and microbiological features of Vibrio vulnificus biogroup 3 causing outbreaks of wound infection and bacteraemia in Israel

Summary Background Vibrio vulnificus is a gram-negative bacterium that causes septicaemia and wound infection. Cases occur sporadically, and no previous outbreaks due to a common source or a clonal strain have been reported. In the summer and autumn of 1996 and 1997, an outbreak of invasive V vulnificus infection occurred in Israel in people who had recently handled fresh, whole fish purchased from artificial fish-ponds. Methods We reviewed clinical and epidemiological information, and undertook an environmental investigation to assess disease characteristics, modes of transmission, phenotypic characteristics of the bacterium, and fish-marketing policy. The clonal nature of 19 isolates was studied by biotyping, pulsed-field gel electrophoresis, and restriction-fragment length polymorphism (RFLP) analysis of a PCR fragment. Findings During 1996–97, 62 cases of wound infection and bacteraemia occurred. 57 patients developed cellulitis, four had necrotising fasciitis, and one developed osteomyelitis. In all cases, the fish were cultivated in inland fish-ponds. In the summer of 1996, fish-pond managers initiated a new marketing policy, in which fish were sold alive instead of being packed in ice. Phenotypically, the isolates had five atypical biochemical test results. The isolates were non-typeable by pulsed-field gel electrophoresis, and all had the same PCR-RFLP pattern which had not been seen previously. Interpretation The cause of the outbreak was a new strain of V vulnificus , classified as biogroup 3. A new fish-marketing policy that began in 1996 may have exposed susceptible people to the organism.

An Outbreak of Yersinia enterocolitica O:8 Infections Associated with Pasteurized Milk

In October 1995, an outbreak of Yersinia enterocolitica O:8 infections occurred in the Upper Valley of Vermont and New Hampshire. Ten patients were identified, median age 9 years (range, 6 months-44 years). Three patients were hospitalized; 1 underwent an appendectomy. Consumption of bottled pasteurized milk from a local dairy was associated with illness (matched odds ratio undefined; lower 95% confidence interval, 1.9). No deficiencies in pasteurization procedures or equipment were detected. Y. enterocolitica O:8 was isolated from 1 raw-milk sample and from a fecal sample from 1 dairy pig. The route of contamination was not determined; this outbreak likely resulted from postpasteurization contamination of milk. Dairy pigs were the most likely source of contamination. Milk bottles were likely contaminated by rinsing with untreated well water prior to filling or by other environmental routes. Educating dairy owners about Y. enterocolitica and postpasteurization contamination is necessary to prevent further outbreaks.

An Outbreak of Foodborne Illness Caused by Escherichia coli O39:NM, an Agent Not Fitting into the Existing Scheme for Classifying Diarrheogenic E. coli

An outbreak of gastrointestinal illness with clinical and epidemiologic features of enterotoxigenic Escherichia coli (ETEC) occurred among patrons of a restaurant during April 1991. Illnesses among several groups of patrons were characterized by diarrhea (100%) and cramps (79%-88%) lasting a median of 3-5 days. Median incubation periods ranged from 50 to 56 h. A nonmotile strain of E. coli (E. coli O39), which was negative for heat-labile (LT) and heat-stable (STa, STb) ETEC toxins, was isolated only from ill patrons. This organism produced enteroaggregative E. coli heat-stable enterotoxin 1 and contained the enteropathogenic E. coli gene locus for enterocyte effacement; it did not display mannose-resistant adherence, but produced attaching and effacing lesions in the absence of mannose on cultured HEp-2 cells. E. coli that are not part of highly characterized but narrowly defined groups may be important causes of foodborne illness.

The use of plasmid profiles and nucleic acid probes in epidemiologic investigations of foodborne, diarrheal diseases

The application of nucleic acid analyses to investigations of infectious disease outbreaks has resulted in useful molecular strain markers that distinguish the epidemic clone of a particular pathogen and help identify specific vehicles of infection. We have successfully used plasmid profile analysis, restriction endonuclease digestion of plasmid and whole-cell DNAs, and nucleic acid hybridization to investigate recent outbreaks of foodborne diarrheal illness. Plasmid analysis has been important in identifying epidemic strains of Salmonella enteritidis and Escherichia coli O157:H7. In a culture survey of S. enteritidis isolates from humans and a variety of animals, including chickens and chicken eggs, we identified 16 distinct plasmid profiles and used these to differentiate strains, especially within commonly occurring phage types (Colindale 8 and 13a). HindIII digests of plasmid DNA were useful in distinguishing plasmids of similar mass but dissimilar enzyme target sequences; they clearly distinguished S. enteritidis strains causing systemic infections in children in parts of Africa from U.S. isolates. Investigations of outbreaks of hemorrhagic colitis have also been assisted by plasmid analysis. Restriction endonuclease digests of whole-cell DNA and Southern blot analysis, hybridizing with E. coli 16S and 23S rRNA (ribotyping), have been effective subtyping techniques, especially for plasmidless isolates of Campylobacter jejuni. In five outbreaks of C. jejuni infections, ribotyping of PvuII and ClaI digests distinguished individual epidemic strains within one commonly occurring C. jejuni serotype (Penner 2, Lior 4). Preliminary data show that ribotyping of NcoI digests can also distinguish individual epidemic strains of E. coli O157:H7 and may provide a more stable marker than plasmid profiles. Specific DNA probes derived from cloned virulence genes of E. coli have been invaluable in epidemic investigations and surveys. Using colony hybridization, we found in one survey of stool specimens from 174 dairy cattle that 11% of animals were asymptomatically carrying Shiga-like toxigenic E. coli other than O157:H7. We also found that newly synthesized oligonucleotide probes for the Shiga-like toxins I and II agreed 100% with cloned gene probes in a study of 613 E. coli strains. Future studies of these organisms will include the use of additional synthetic oligonucleotides as primers to amplify the toxin genes directly in patient and animal specimens by the polymerase chain reaction. There is a continuing and expanding role for molecular approaches in epidemiological investigations. The DNA methods described above are not based on the often complex expression of phenotypic characteristics, and, unlike sensitive and specific techniques such as phage typing, a single method can be used to study a variety of Gram-positive and negative bacterial pathogens.

Salmonella enteritidis Gastroenteritis Transmitted by Intact Chicken Eggs

OBJECTIVE To determine the source and to describe the clinical importance of a large outbreak of Salmonella enteritidis gastroenteritis in Tennessee, which is outside the geographic focus of the S. enteritidis pandemic. DESIGN A case-control study and tracing of the source eggs. SETTING A Tennessee community and a large layer farm in Indiana. PATIENTS Case patients ate at the implicated restaurant and subsequently developed S. enteritidis gastroenteritis; controls ate with the case patients, but did not develop gastroenteritis. MEASUREMENTS Eighty-one case patients were identified; 73 (90%) had eaten egg-containing sauces at a local restaurant on a given evening. The eggs were traced to their farm of origin in Indiana. The farm was inspected 5 weeks after the outbreak. MAIN RESULTS Of 24 patients with culture-proved cases, 11 were hospitalized. Hollandaise and bernaise sauces prepared with intact, extra-large, grade-A eggs were strongly associated with illness (P less than 0.001). Salmonella enteritidis was isolated from specimens collected from chickens and the farm. Antimicrobial susceptibility patterns, phage typing, and plasmid profiles of isolates from the farm and from patients were indistinguishable. CONCLUSIONS Salmonella enteritidis infection is a large and growing public health problem that is spreading beyond the northeastern United States. This study shows a direct link between infected poultry flocks and an outbreak of human illness.

Cholera in the United States, 1995–2000: Trends at the End of the Twentieth Century

To evaluate recent trends in cholera in the United States, surveillance data from all cases of laboratory-confirmed toxigenic Vibrio cholerae O1 and O139 infection reported to the Centers for Disease Control and Prevention between 1995 and 2000 were reviewed. Sixty-one cases of cholera, all caused by V. cholerae O1, were reported. There was 1 death, and 35 (57%) of the patients were hospitalized. Thirty-seven (61%) infections were acquired outside the United States; 14 (23%) were acquired through undercooked seafood consumed in the United States, 2 (3%) were acquired through sliced cantaloupe contaminated by an asymptomatically infected food handler, and no source was identified for 8 (13%) infections. The proportion of travel-associated infections resistant to trimethoprim-sulfamethoxazole, sulfisoxazole, streptomycin, and furazolidone increased from 7 (8%) of 88 in 1990-1994 to 11 (31%) of 35 in 1995-2000. Foreign travel and undercooked seafood continue to account for most US cholera cases. Antimicrobial resistance has increased among V. cholerae O1 strains isolated from ill travelers.

A Prolonged Outbreak of Shigella sonnei Infections in Traditionally Observant Jewish Communities in North America Caused by a Molecularly Distinct Bacterial Subtype

During 1994-1996, Shigella sonnei outbreaks occurred in 8 North American traditionally observant Jewish communities. These communities remain relatively separate from neighboring populations while maintaining close contact by travel with coreligionists in other cities. Epidemiologic investigations suggested community-to-community transmission via travel. Outbreak-related and control isolates of S. sonnei from each city were subtyped by pulsed-field gel electrophoresis (PFGE) to confirm an epidemiologic linkage between outbreaks. Forty-three (94%) of 46 outbreak-related isolates had closely related PFGE patterns, constituting a single subtype; 33 (94%) of 35 control isolates demonstrated unrelated PFGE patterns. Several patterns differing by < or = 3 bands were identified within the outbreak subtype; one of these accounted for 65% of outbreak isolates. Hence, a single subtype of S. sonnei caused an international outbreak involving 8 traditionally observant Jewish communities, but not neighboring populations, over a 2-year period, suggesting sustained propagation of the epidemic strain between communities.

Seasonal, nontoxigenic Vibrio cholerae 01 Ogawa infections in the Eastern Region of Saudi Arabia

BACKGROUND Surveillance for Vibrio cholerae in the Eastern Region of Saudi Arabia has been ongoing since 1985 to detect and prevent local proliferation of imported cholera. In 1996 and 1997 the authors performed additional microbiologic and epidemiologic assessment of V. cholerae surveillance to better characterize a recurrent summertime pattern of V. cholerae infections in the Eastern Region of Saudi Arabia. METHODS All health facilities routinely submitted stool or rectal swab specimens for isolation of V. cholerae from patients with gastroenteritis. In addition, specimens were taken from expatriate workers and household contacts of persons with confirmed V. cholerae infection. Forty-two isolates were evaluated for cholera enterotoxin by enzyme-linked immunosorbent assay, cholera toxin polymerase chain reaction, and Y1 adrenal cell assay; 12 isolates also were characterized by pulsed-field gel electrophoresis (PFGE). Interviews about potential exposures were done for all V. cholerae infections. RESULTS Vibrio cholerae O1 serotype Ogawa biotype El Tor was identified in 113 gastroenteritis patients (6.0 per 100,000 population per year), 28 asymptomatic expatriate workers, and 16 of 982 household contacts of index patients. All symptomatic infected persons had mild illness that was not typical of cholera, and all 42 isolates evaluated were nontoxigenic. All 12 isolates evaluated by PFGE had an indistinguishable pattern (pattern 81). Infections appeared in late May, decreased in mid-July through August, increased again in September, and disappeared from December through April. Infections had a uniform geographic distribution and affected all ages. No linkage was identified between affected households, or between community cases and food-handlers or domestic servants. DISCUSSION Surveillance in the Eastern Region of Saudi Arabia has identified a novel strain of nontoxigenic V. cholerae O1 Ogawa. This strain probably has a local environmental reservoir. Since cholera toxin is the primary virulence factor involved in the cause of cholera, assays for cholera toxin should be included in cholera surveillance.