Laurence Slutsker

Practice Guidelines for the Management of Infectious Diarrhea

The widening array of recognized enteric pathogens and the increasing demand for cost-containment sharpen the need for careful clinical and public health guidelines based on the best evidence currently available. Adequate fluid and electrolyte replacement and maintenance are key to managing diarrheal illnesses. Thorough clinical and epidemiological evaluation must define the severity and type of illness (e.g., febrile, hemorrhagic, nosocomial, persistent, or inflammatory), exposures (e.g., travel, ingestion of raw or undercooked meat, seafood, or milk products, contacts who are ill, day care or institutional exposure, recent antibiotic use), and whether the patient is immunocompromised, in order to direct the performance of selective diagnostic cultures, toxin testing, parasite studies, and the administration of antimicrobial therapy (the latter as for travelers diarrhea, shigellosis, and possibly Campylobacter jejuni enteritis). Increasing numbers of isolates resistant to antimicrobial agents and the risk of worsened illness (such as hemolytic uremic syndrome with Shiga toxin-producing Escherichia coli O157:H7) further complicate antimicrobial and antimotility drug use. Thus, prevention by avoidance of undercooked meat or seafood, avoidance of unpasteurized milk or soft cheese, and selected use of available typhoid vaccines for travelers to areas where typhoid is endemic are key to the control of infectious diarrhea.

A Research Agenda to Underpin Malaria Eradication

Pedro Alonso and colleagues introduce the Malaria Eradication Research Agenda (malERA) initiative and the set of articles published in this PLoS Medicine Supplement that distill the research questions key to malaria eradication.

Vibrio parahaemolyticus Infections in the United States, 1973–1998

Vibrio parahaemolyticus infections are associated with consumption of raw or undercooked shellfish, contaminated food, and exposure of wounds to warm seawater. Foodborne outbreaks and sporadic infections from Vibrio species in 4 Gulf Coast states are reported routinely to the Centers for Disease Control and Prevention (CDC). Between 1988 and 1997, 345 sporadic V. parahaemolyticus infections were reported: 59% were gastroenteritis, 34% were wound infections, 5% were septicemia, and 2% were from other exposures. Forty-five percent of patients suffering from these conditions were hospitalized for their infections, and 88% of persons with acute gastroenteritis reported having eaten raw oysters during the week before their illness occurred. Between 1973 and 1998, 40 outbreaks of V. parahaemolyticus infections were reported to the CDC, and these outbreaks included >1000 illnesses. Most of these outbreaks occurred during the warmer months and were attributed to seafood, particularly shellfish. The median attack rate among persons who consumed the implicated seafood was 56%. To prevent V. parahaemolyticus infections, persons should avoid consumption of raw or undercooked shellfish and exposure of wounds to seawater.

An Outbreak of Escherichia coli O157:H7 Infections Associated with Leaf Lettuce Consumption

In July 1995, 40 Montana residents were identified with laboratory-confirmed Escherichia coli O157:H7 infection; 52 residents had bloody diarrhea without laboratory confirmation. The median age of those with laboratory-confirmed cases was 42 years (range, 4- 86); 58% were female. Thirteen patients were hospitalized, and 1 developed hemolytic-uremic syndrome. A case-control study showed that 19 (70%) of 27 patients but only 8 (17%) of 46 controls reported eating purchased (not home-grown) leaf lettuce before illness (matched odds ratio, 25.3; 95% confidence interval, 3.9-1065.6). Pulsed-field gel electrophoresis identified a common strain among 22 of 23 isolates tested. Implicated lettuce was traced to two sources: a local Montana farm and six farms in Washington State that shipped under the same label. This outbreak highlights the increasing importance of fresh produce as a vehicle in foodborne illness. Sanitary growing and handling procedures are necessary to prevent these infections.

A National Outbreak of Salmonella enteritidis Infections from Ice Cream

BACKGROUND In September 1994, the Minnesota Department of Health detected an increase in the number of reports of Salmonella enteritidis infections. After a case-control study implicated a nationally distributed brand of ice cream (Schwans) in the outbreak, the product was recalled and further epidemiologic and microbiologic investigations were conducted. METHODS We defined an outbreak-associated case of S. enteritidis infection as one in which S. enteritidis was cultured from a person who became ill in September or October 1994. We established national surveillance and surveyed customers of the implicated manufacturer. The steps involved in the manufacture of ice cream associated with cases of S. enteritidis infection were compared with those of products not known to be associated with infection matched for the date of manufacture. Cultures for bacteria were obtained from ice cream samples, the ice cream plant, and tanker trailers that had transported the ice cream base (premix) to the plant. RESULTS We estimate that S. enteritidis gastroenteritis developed in 224,000 persons in the United States after they ate Schwans ice cream. The attack rate for consumers was 6.6 percent. Ice cream associated with infection contained a higher percentage of premix that had been transported by tanker that had carried nonpasteurized eggs immediately before (P = 0.02). S. enteritidis was isolated from 8 of 226 ice cream products (3 percent), but not from environmental samples obtained from the ice cream plant (n = 157) or tanker trailers (n = 204). CONCLUSIONS This nationwide outbreak of salmonellosis was most likely the result of contamination of pasteurized ice cream premix during transport in tanker trailers that had previously carried nonpasteurized liquid eggs containing S. enteritidis. To prevent further outbreaks, food products not destined for repasteurization should be transported in dedicated containers.

An international outbreak of Salmonella infections caused by alfalfa sprouts grown from contaminated seeds

An outbreak of Salmonella serotype stanley infections occurred in the United States and Finland in 1995. The outbreak was investigated through case-control studies in Arizona, Michigan, and Finland; by isolate subtyping; and by tracing and culturing of the implicated food. Alfalfa sprout consumption was the only exposure associated with S. stanley infections in Arizona (matched odds ratio [MOR] = 11.1; 95% confidence interval [CI], 1.4-513), Michigan (MOR = 5.5; CI, 1.6-23), and Finland (MOR undefined; CI, 4.9-infinity). US and Finnish patient isolates were a unique outbreak strain distinct from S. stanley isolates not linked to the outbreak. Alfalfa sprouts eaten by patients in 6 US states and Finland were traced to seed shipped by a Dutch shipper. Thus, it was concluded that alfalfa sprouts grown from contaminated seed caused an international outbreak of > or =242 S. stanley infections in > or =17 US states and Finland. This outbreak illustrates a new mechanism through which contamination of fresh produce can cause large, widely dispersed outbreaks.

The Changing Epidemiology of Salmonella: Trends in Serotypes Isolated from Humans in the United States, 1987–1997

Salmonellosis is a major cause of illness in the United States. To highlight recent trends, data for 1987-1997 from the National Salmonella Surveillance System were analyzed. A total of 441,863 Salmonella isolates were reported, with the highest age-specific rate among infants (159/100,000 infants at 2 months). Annual isolation rates decreased from 19 to 13/100,000 persons; however, trends varied by serotype. The isolation rate of Salmonella serotype Enteritidis increased until 1996, whereas declines were noted in Salmonella serotypes Hadar and Heidelberg. Overall, serotypes that increased in frequency were significantly more likely than those that decreased to be associated with reptiles (P=.008). Salmonella infections continue to be an important cause of illness, especially among infants. Recent declines in food-associated serotypes may reflect changes in the meat, poultry, and egg industries that preceded or anticipated the 1996 implementation of pathogen-reduction programs. Additional educational efforts are needed to control the emergence of reptile-associated salmonellosis.

Operational strategies to achieve and maintain malaria elimination

Summary Present elimination strategies are based on recommendations derived during the Global Malaria Eradication Program of the 1960s. However, many countries considering elimination nowadays have high intrinsic transmission potential and, without the support of a regional campaign, have to deal with the constant threat of imported cases of the disease, emphasising the need to revisit the strategies on which contemporary elimination programmes are based. To eliminate malaria, programmes need to concentrate on identification and elimination of foci of infections through both passive and active methods of case detection. This approach needs appropriate treatment of both clinical cases and asymptomatic infections, combined with targeted vector control. Draining of infectious pools entirely will not be sufficient since they could be replenished by imported malaria. Elimination will thus additionally need identification and treatment of incoming infections before they lead to transmission, or, more realistically, embarking on regional initiatives to dry up importation at its source.

Case-control study of an acute aflatoxicosis outbreak, Kenya, 2004

Objectives: During January–June 2004, an aflatoxicosis outbreak in eastern Kenya resulted in 317 cases and 125 deaths. We conducted a case–control study to identify risk factors for contamination of implicated maize and, for the first time, quantitated biomarkers associated with acute aflatoxicosis. Design: We administered questionnaires regarding maize storage and consumption and obtained maize and blood samples from participants. Participants: We recruited 40 case-patients with aflatoxicosis and 80 randomly selected controls to participate in this study. Evaluations/Measurements: We analyzed maize for total aflatoxins and serum for aflatoxin B1–lysine albumin adducts and hepatitis B surface antigen. We used regression and survival analyses to explore the relationship between aflatoxins, maize consumption, hepatitis B surface antigen, and case status. Results: Homegrown (not commercial) maize kernels from case households had higher concentrations of aflatoxins than did kernels from control households [geometric mean (GM) = 354.53 ppb vs. 44.14 ppb; p = 0.04]. Serum adduct concentrations were associated with time from jaundice to death [adjusted hazard ratio = 1.3; 95% confidence interval (CI), 1.04–1.6]. Case patients had positive hepatitis B titers [odds ratio (OR) = 9.8; 95% CI, 1.5–63.1] more often than controls. Case patients stored wet maize (OR = 3.5; 95% CI, 1.2–10.3) inside their homes (OR = 12.0; 95% CI, 1.5–95.7) rather than in granaries more often than did controls. Conclusion: Aflatoxin concentrations in maize, serum aflatoxin B1–lysine adduct concentrations, and positive hepatitis B surface antigen titers were all associated with case status. Relevance: The novel methods and risk factors described may help health officials prevent future outbreaks of aflatoxicosis.

Escherichia coli O157: H7 Diarrhea in the United States: Clinical and Epidemiologic Features

Escherichia coli O157:H7 was first recognized as a human pathogen in 1982 [1], and it is increasingly recognized as an important cause of sporadic and outbreak-associated bloody diarrhea [2]. Strains of E. coli O157:H7 are characterized by their ability to produce moderate or large amounts of two types of Shiga toxin. These toxins are important factors in the pathogenesis of postdiarrheal hemolytic uremic syndrome, and E. coli O157:H7 infection is the major cause of this syndrome in children in the United States and Canada [3-6]. Outbreaks of E. coli O157:H7 have involved communities [7-9] and such institutions as nursing homes [10, 11], schools [12], and day care facilities [13, 14]. Routine stool cultures do not identify E. coli O157:H7. Unlike 80% of E. coli serotypes, however, E. coli O157:H7 does not rapidly ferment D-sorbitol and therefore appears colorless on sorbitol-MacConkey agar culture plates read at 24 hours [15, 16]. These sorbitol-negative colonies can then be screened for agglutination in O157 antiserum. Relatively little information is available about the frequency of isolation of E. coli O157:H7 from ill persons in the United States; most U.S. laboratories do not routinely culture for this organism [17]. In single-center studies in the United States in which all stool specimens were cultured for this organism, isolation rates ranged from 0.08% to 0.5% [18-20]. Recent information suggests that E. coli O157:H7 has been isolated from patients in most states [21], but the frequency of this isolation compared with that of other enteric pathogens in different geographic areas during similar time periods has not been described. The reported clinical signs and symptoms of E. coli O157:H7 infection include bloody or nonbloody diarrhea, abdominal cramps, and lack of reported fever [22, 23]. However, this information was derived from relatively few persons in outbreak settings, and few studies have examined the clinical presentation of illness due to E. coli O157:H7 infection compared with the clinical presentation of illness due to other bacterial enteric pathogens. We therefore sought to determine 1) the frequency of isolation of E. coli O157:H7 and 2) the clinical and epidemiologic features of infections with E. coli O157:H7 compared with those of Campylobacter, Salmonella, and Shigella species at 10 hospitals located throughout the United States. Using standard microbiological methods, we assessed the ways in which time of year, geographic location, and the demographic and clinical features of patients affected the likelihood of isolation of these enteric pathogens. Methods Study Sample Our study was announced and participation was requested in a newsletter that was sent to hospitals in the National Nosocomial Infections Surveillance system [24]. Five hospitals in this system and five other hospitals were chosen on the basis of geographic location, willingness to participate, receipt of specimens in a primary care setting, and the expectation that an adequate number of outpatient stool cultures would be done each year. All four census divisions of the United States were represented. Nine hospitals served general patient populations that included all age groups, and one served a primarily pediatric population. All served both inpatients and outpatients. The average annual number of stool specimens screened by each hospital ranged from 400 to 4000 (median, 1300). Four of the hospitals were university hospitals, and six were community hospitals. At each hospital, all of the specimens studied were fecal samples from inpatients and outpatients of all ages that were submitted to the clinical microbiology laboratory for routine pathogen identification. The study was conducted from October 1990 through October 1992. Collection and Handling of Specimens All sites agreed to use the following methods for the collection and handling of specimens. Swabs were transported in Cary-Blair transport medium, Amies transport medium, or Stuart transport medium and were streaked immediately onto plating media or were kept at 4 C for no more than 24 hours. If whole stool specimens were not examined within 1 hour of receipt by the laboratory, a swab of the stool was placed in transport medium, refrigerated, and examined within 24 hours. Specimens were visually inspected for gross blood, and the presence of occult blood was determined by using the hemoccult test. The presence of fecal leukocytes was determined by placing a bit of stool in a drop of methylene blue on a slide or by doing a Gram stain and examining the specimen using the high-power microscope objective. Specimens were graded as having 0, 1 to 4, 5 to 9, or 10 or more leukocytes per high-power field. Standard methods were used to isolate and identify Campylobacter, Salmonella, and Shigella species. Other assays, such as those for Clostridium difficile or rotavirus, were not part of the protocol and were done according to the routines of the individual site laboratories and the physicians ordering the tests. Isolation of Escherichia coli O157:H7 Before the study began, each laboratory received control strains of E. coli O157:H7 and instructions about the isolation and identification of this organism. To identify E. coli O157:H7, fecal specimens were plated onto sorbitol-MacConkey agar and the plates were incubated at 37 C for 24 hours. Three sorbitol-negative colonies were tested for agglutination with O157 latex reagents (Pro-Lab, Inc., Round Rock, Texas). The O157-positive colonies were sent to the Centers for Disease Control and Prevention for biochemical identification and serotyping [25]. Isolates confirmed as E. coli O157:H7 or O157:NM (nonmotile) were tested for production of Shiga toxin 1 and 2 (formerly called Shiga-like toxins I and II [26]) and for the presence of Shiga toxin genes by hybridization with oligonucleotide probes [27]. Isolates were tested by using the disk diffusion technique [28] for susceptibility to a standard panel of antimicrobial agents [28]. Data Collection For each fecal specimen received, data were entered on a standard line list; only the first specimen from each patient was included. The information collected for each specimen included date obtained, date plated, source (whole stool or swab), presence of visible or occult blood, presence and quantity of fecal leukocytes, and presence of pathogens. After permission was obtained from the relevant health care provider, a clinical data form was completed through retrospective chart review for all patients from whom Campylobacter, Salmonella, or Shigella species or E. coli O157:H7 were isolated and from every 25th patient from whom no pathogen was isolated. Information obtained included age, sex, date of the onset of illness, inpatient or outpatient status, symptoms (including presence and date of onset of diarrhea, bloody stools, abdominal pain, vomiting, and fever in the previous 2 weeks), abdominal tenderness, largest number of bowel movements in a 24-hour period, maximum body temperature on the day of culture (as measured by a health practitioner), peripheral blood leukocyte count, and whether the patient was admitted to the hospital. If a patient had a body temperature of at least 37.8 C, he or she was considered to have fever. Data Analysis Salmonella, Shigella, and Campylobacter species and E. coli O157:H7 were considered to be major bacterial enteric pathogens. Isolates that were identified as O157:H7 or O157:NM and that produced Shiga toxin were considered to be strains of E. coli O157:H7. An isolation proportion for a pathogen was defined as the proportion of all fecal specimens that yielded that pathogen. To estimate the age-specific isolation proportion of pathogens from stool specimens, we divided the number of persons in each age group for whom a specific pathogen was isolated by the sum of all persons (both culture-positive and culture-negative) in that age group. We estimated the total number of culture-negative persons in each age group by extrapolating the age group distribution frequency from the sample of culture-negative persons for whom age was known to all culture-negative persons. For the analysis of clinical features associated with infection, patients whose stool cultures yielded more than one bacterial pathogen were excluded. Differences in proportions were analyzed using a chi-square test or the Fisher exact test. For normally distributed data, differences in means were compared using the Student t-test; for nonparametric data, differences in medians were compared using the Wilcoxon two-sample test. Logistic regression analysis was done using generalized estimating equations to assess factors independently associated with E. coli O157:H7 infection while controlling for study site. For all statistical tests, a two-tailed P value less than 0.05 was considered significant. Results Isolation of Pathogens During the study period, fecal specimens from 30 463 persons were examined. A source was specified for 29 355 of these specimens; 63% were from whole stools and 37% were from swabs. Overall, 1708 of the specimens (5.6%) yielded at least one of the four major bacterial enteric pathogens; for 27 902 specimens (91.6%), no pathogen was isolated. Eleven patients had dual infections: Six had Shigella species and Campylobacter species infections, 3 had Salmonella species and Campylobacter species infections, and 2 had Shigella species and Salmonella species infections. The highest isolation proportions from fecal specimens for E. coli O157:H7 were seen in hospitals in Maine and Wisconsin; the lowest proportion was seen in Virginia (Table 1). Of the four bacterial pathogens, E. coli O157:H7 was the second most frequently isolated in Maine, the third most frequently isolated (ahead of Shigella species) in Washington and Wisconsin, and the third most frequently isolated (tied with Shigella species) in Michigan. In the hospitals in northern states (Maine, Michigan, New