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PubMed1999

Two outbreaks of multidrug-resistant Salmonella serotype typhimurium DT104 infections linked to raw-milk cheese in Northern California.

CONTEXT: Salmonella serotype Typhimurium definitive type 104 (DT104), with resistance to 5 drugs (ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline), has emerged as the most common multidrug-resistant Salmonella strain in the United States. However, illnesses resulting from this strain have not been associated definitively with a source in this country. OBJECTIVE: To determine the source of 2 outbreaks of Salmonella Typhimurium DT104. DESIGN: Matched case-control study conducted between March 24 and April 5, 1997 (outbreak 1), enhanced surveillance for new cases dating from February 1, 1997 (outbreak 2), and environmental and laboratory investigations. SETTING AND PARTICIPANTS: The case-control study included residents of 2 adjacent counties in northern California infected with the outbreak strain of Salmonella Typhimurium var Copenhagen and age-matched controls. For enhanced surveillance, a case was defined as Salmonella Typhimurium infection in a person exposed to fresh Mexican-style cheese. MAIN OUTCOME MEASURES: Risk factors for infection and source of implicated food. RESULTS: Outbreak 1 peaked in February 1997; 31 patients were confirmed by culture as having Salmonella Typhimurium var Copenhagen infection, isolates of which showed indistinguishable pulsed-field gel electrophoresis (PFGE) patterns. The outbreak strain was phage type DT104 with the 5-drug resistance pattern. Sixteen cases and 25 controls were enrolled in the case-control study; 15 of 16 Salmonella Typhimurium var Copenhagen cases compared with 14 of 24 matched controls reported eating unpasteurized Mexican-style cheese, (matched odds ratio, 7.9; 95% confidence interval, 1.1-354.9). Enhanced surveillance uncovered outbreak 2, which peaked in April 1997 and was caused by a non-Copenhagen variant of Salmonella Typhimurium. During outbreak 2, Salmonella Typhimurium was isolated from 79 persons who ate fresh Mexican-style cheese from street vendors and from cheese samples and raw milk. The PFGE pattern of the milk isolate matched 1 of the 3 patterns recovered from patients; all strains were phage type DT104b with the 5-drug resistance pattern. CONCLUSION: Raw-milk products pose a risk for multidrug-resistant Salmonella Typhimurium DT104 infections.

Adolescent↗
PubMed2005

Norovirus genotypes causing gastroenteritis outbreaks in Finland 1998-2002.

BACKGROUND: Outbreak investigation methods for enteric viruses were improved in 1990s when gene amplification techniques were established in viral laboratories. OBJECTIVES: The objective of the study was to determine the causative agents for Finnish viral gastroenteritis outbreaks. Our aim was also to further characterise the norovirus strains, reveal the temporal occurrence of norovirus (NV) genotypes and to study some epidemiological aspects concerning the outbreaks. STUDY DESIGN: A total of 416 Finnish viral gastroenteritis outbreaks that occurred during 5 years (1998-2002), excluding those among hospitalised children, were investigated for enteric viruses. Stool samples were screened by electron microscopy as well as analyzed by specific noro- and astrovirus RT-PCR tests. Amplicon sequence analysis was used to find out norovirus genotypes. RESULTS: Noroviruses caused 252 (60.6%) of the outbreaks; other viruses, astro- or rotavirus, caused four epidemics. Norovirus epidemics occurred in all kinds of settings, most often in hospitals (30.6%) and in restaurants and canteens (14.3%). Both NV genogroups were found every year, but NV GGII outbreaks always outnumbered those of GGI. All but one outbreak at hospitals and nursing homes were of genotype GII. Polymerase sequence analysis revealed a variety of NV genotypes; six GI and at least eight GII genotypes. The GI.3 Birmingham-like and GII.4 Bristol-like genotype appeared every year, whereas the other types were circulating for shorter periods or sporadically. During the study period the genotypes GII.4 (Bristol), GII.1 (Hawaii), an emerging genotype GIIb, and a new variant of GII.4 predominated in that order. Indication for rapid genetic changes in the genotype GII.4 was also noticed. CONCLUSIONS: Noroviruses were the most prevalent causative agents in the outbreaks. Many NV genotypes were circulating, and a shift in the predominant genotypes was evident between epidemic seasons.

Caliciviridae Infections↗
PubMed2005

Additional value of typing Noroviruses in gastroenteritis outbreaks in Amsterdam, The Netherlands.

BACKGROUND: In Amsterdam, 17 of the 55 gastroenteritis (GI) outbreaks reported from January 2002 to May 2003 were confirmed to be caused by noroviruses (NV). OBJECTIVE: In this study, we describe the molecular epidemiology of a group of nine outbreaks associated with a catering firm and two outbreaks, 5 months apart, in an Amsterdam hospital. All outbreaks were typed to confirm their linkage, and the hospital-related cases were studied to see if the two outbreaks were caused by one persisting NV strain or by a reintroduction after 5 months. RESULTS AND CONCLUSIONS: For the outbreaks associated with the catering firm one NV genogroup I strain was found which was identical in sequence among customers and employees of the caterer. This was not the strain that predominantly circulated in 2002/2003 in and around Amsterdam, which was the NV genogroup II4 "new variant" (GgII4nv) strain. In the Amsterdam hospital, the two outbreaks were caused by this predominant GgII4nv type, and we argue that NV was most likely reintroduced in the second outbreak from the Amsterdam community.

Caliciviridae Infections↗
PubMed2003

One predominant type of genetically closely related Shigella sonnei prevalent in four sequential outbreaks in school children.

Seventy-six Shigella sonnei isolates from four sequential outbreaks in school children were analyzed to determine their relatedness. Outbreak strains exhibited two major antibiograms, 9 plasmid profiles, 10 enterobacterial repetitive intergenic consensus sequence (ERIC)-PCR patterns, and 17 pulsed-field gel electrophoresis (PFGE) patterns. Of typing methods, ERIC-PCR types generally coincided with the PFGE types within these outbreak strains. However, ERIC-PCR analysis could not discriminate an epidemiologically unrelated strain from some outbreak strains. Further computer-assisted analysis for similarity of the PFGE patterns revealed that the main culprits of these four sequential outbreaks were strains of pulsotype C (88.2% of total outbreak isolates). The results indicate that PFGE can provide more explicit relatedness of outbreak strains than the other typing methods examined. In conclusion, based on PFGE analysis, one predominant pulsotype of multiple genetically related strains of S. sonnei was prevalent in these four sequential outbreaks.

Anti-Bacterial Agents↗
PubMed1985

How frequent are outbreaks of nosocomial infection in community hospitals?

A statistical algorithm was used to identify potentially important clusters among nosocomial infections reported each month by 7 community hospitals. Epidemiologic review and on-site investigations distinguished outbreaks of clinical disease from factitious clusters. In 1 year, 8 outbreaks were confirmed. They involved 82 patients--approximately 2% of patients with nosocomial infections and 0.09% of all discharges. One true outbreak occurred for every 12,000 discharges--at least 1 outbreak per year for the average community hospital. Five (63%) outbreaks were recognized independently by the hospitals' infection control personnel. Four (50%) resolved spontaneously; the hospitals' own control measures were necessary in 2; and 2 resolved only after an outside investigation. Organized surveillance appears necessary to detect some outbreaks, and control measures are needed to stop many. Since, however, outbreaks account for such a small proportion of nosocomial infections, infection control programs should be sufficiently staffed and managed so that most of the effort is directed toward the surveillance and control of endemic infection problems, but with adequate resources remaining to respond to outbreaks when they occur.

Cross Infection↗
PubMed2000

Strengths and limitations of molecular subtyping in a community outbreak of Legionnaires' disease.

An epidemiological and microbiological investigation of a cluster of eight cases of Legionnaires' disease in Los Angeles County in November 1997 yielded conflicting results. The epidemiological part of the investigation implicated one of several mobile cooling towers used by a film studio in the centre of the outbreak area. However, water sampled from these cooling towers contained L. pneumophila serogroup 1 of another subtype than the strain that was recovered from case-patients in the outbreak. Samples from two cooling towers located downwind from all of the case-patients contained a Legionella strain that was indistinguishable from the outbreak strain by four subtyping techniques (AP-PCR, PFGE, MAb, and MLEE). It is unlikely that these cooling towers were the source of infection for all the case-patients, and they were not associated with risk of disease in the case-control study. The outbreak strain also was not distinguishable, by three subtyping techniques (AP-PCR, PFGE, and MAb), from a L. pneumophila strain that had caused an outbreak in Providence, RI, in 1993. Laboratory cross-contamination was unlikely because the initial subtyping was done in different laboratories. In this investigation, microbiology was helpful for distinguishing the outbreak cluster from unrelated cases of Legionnaires' disease occurring elsewhere. However, multiple subtyping techniques failed to distinguish environmental sources that were probably not associated with the outbreak. Persons investigating Legionnaires' disease outbreaks should be aware that microbiological subtyping does not always identify a source with absolute certainty.

Adult↗
PubMed2000

Modelling the impact of prior immunity, case misclassification and bias on case-control studies in the investigation of outbreaks of cryptosporidiosis.

Cryptosporidiosis is the most common cause of outbreaks of disease linked to mains water supply in the United Kingdom and the second commonest in the United States. Recent evidence has suggested that prior population immunity may have an impact on the epidemiology of waterborne outbreaks and in particular prior immunity may reduce the power of case-control studies for demonstrating association between disease and water consumption behaviour. However, the degree of impact of prior immunity on the power of epidemiological studies is not yet clear. This paper reports the results of some simple mathematical models of outbreaks of waterborne disease in populations with varying levels of immunity due to prior water and non-water exposure. The basic outbreak model was run on a spreadsheet. To determine the impact of prior immunity on case-control studies, further analysis was done using a Monte Carlo method to simulate sampling from cases and controls. It was found that moderate degrees of prior immunity due to water associated disease could markedly reduce the relative risk of water consumption on illness in waterborne outbreaks. In turn this would reduce the power of case-control studies. In addition, this model was used to demonstrate the impact of case misclassification and recall bias on case-control studies. Again it was found that within the model, the results of case-control studies could be significantly affected by both these sources of error. Anyone conducting epidemiological investigations of potentially waterborne outbreaks of disease should be aware of the epidemiological problems. Mistakes from case-control studies will be minimized if the outbreak team pays considerable attention to the descriptive phase of the investigation and if case-control studies are conducted as soon as possible after an outbreak is detected.

Adolescent↗
PubMed2001

Epidemiologic profiling: evaluating foodborne outbreaks for which no pathogen was isolated by routine laboratory testing: United States, 1982-9.

The objective was to evaluate foodborne outbreaks of undetermined aetiology by comparing them to pathogen-specific epidemiologic profiles of laboratory-confirmed foodborne outbreaks. National foodborne outbreak data reported to CDC during 1982-9 were categorized by clinico-epidemiologic profiles based on incubation, duration, percent vomiting, fever and vomiting to fever ratio. From the pathogen-specific profiles, five syndromes were developed: a vomiting-toxin syndrome resembling Bacillus cereus and Staphylococcus aureus; a diarrhoea-toxin syndrome characteristic of Clostridium perfringens, a diarrhaeogenic Escherichia coli syndrome, a Norwalk-like virus syndrome, and a salmonella like syndrome. Of 712 outbreaks, 624 (87.6%) matched one of five syndromes; 340 (47.8%) matched the Norwalk-like syndrome and 83 (11.7%) matched the salmonella-like syndrome. After combining information on known pathogens and epidemiologic profiles, only 88 (12.4%) outbreaks remained unclassified. Norwalk-like virus outbreaks appear as common as salmonella-like outbreaks. We conclude that profiling can help classify outbreaks, guide investigations and direct laboratory testing to help detect new and emerging pathogens.

Algorithms↗
PubMed2002

A community survey of self-reported gastroenteritis undertaken during an outbreak of cryptosporidiosis strongly associated with drinking water after much press interest.

We took the opportunity provided by a large outbreak of cryptosporidiosis in the North West of England to investigate the potential impact of recall bias on strength of association and on estimates of outbreak size. We conducted a community-based survey of 4 towns within the outbreak area and 4 control towns. A postal questionnaire was sent to 120 homes, chosen at random from the local telephone directory, in each of the 8 towns. Although not statistically significant, the prevalence of self-reported diarrhoeal disease was marginally higher in the control towns than in the outbreak towns. There was a very strong association between self-reported diarrhoea and drinking water consumption in both control and outbreak areas. The impact of recall bias in outbreak investigations is much greater than previously thought. Identification of the cause of outbreaks should not be based solely on case-control studies conducted after the press has reported the outbreak. Such evidence is likely to be unreliable and give falsely significant associations between water consumption and disease.

Bias↗
PubMed2006

An outbreak of human salmonellosis caused by ampicillin-resistant Salmonella enterica serovar Enteritidis PT13 in the Czech Republic.

In summer 2004, an outbreak caused by Salmonella enterica serovar Enteritidis phage type 13 (S. Enteritidis PT13) was recorded in the Czech Republic. As well being a relatively rare phage type the strain was also ampicillin resistant. Outbreak (n=39) and pre-outbreak isolates (n=13) were characterized by pulsed-field gel electrophoresis (PFGE), beta-lactamase gene polymerase chain reaction and plasmid profile. The majority of outbreak isolates (n=37) were identical in XbaI PFGE profile, and two other outbreak isolates each differed from this profile by one or two fragments respectively. The pre-outbreak isolates were uniform in PFGE profile but distinct from the outbreak strain. Ampicillin resistance was confirmed to be encoded by the blaTEM gene located on the TnA transposon. This gene was readily transferable to a S. Enteritidis recipient strain and was associated with the transfer of a 200-kb plasmid. Our results indicate that all S. Enteritidis PT13 tested from 2004 belonged to a single outbreak strain which prior to 2004 had not been recognized in the Czech Republic.

Ampicillin↗
PubMed2002

Use of oseltamivir during influenza outbreaks in Ontario nursing homes, 1999-2000.

OBJECTIVES: To describe the experience of Ontario long-term care facilities that used oseltamivir during influenza outbreaks in 1999/2000. DESIGN: Case series. SETTING: Ten Ontario long-term care facilities for older people and their residents. PARTICIPANTS: Older residents of long-term care facilities. INTERVENTION: Oseltamivir for treatment or prophylaxis during 11 influenza outbreaks in 1999/2000. MEASUREMENTS: Control of outbreaks; pneumonia, hospitalization, and death complicating acute influenza. RESULTS: All outbreaks were due to influenza A//H3N2/Sydney/05/97. One facility elected to use oseltamivir for treatment and amantadine for prophylaxis. The remaining nine facilities (10 outbreaks) recommended oseltamivir for treatment and prophylaxis (after amantadine failure in five and as primary prophylaxis in five). Use of oseltamivir was associated with termination of the outbreak in all eight evaluable outbreaks. Overall, 178/185 (96%) case-residents met the case definition of influenza and had complete data for evaluation. Of these, 63 (35%) were treated with antibiotics, 37 (21%) were diagnosed with pneumonia, 19 (11%) were hospitalized, and 16 (9%) died. Compared with residents receiving no therapy or who became ill while taking amantadine, residents who received oseltamivir within 48 hours of the onset of symptoms were less likely to be prescribed antibiotics, to be hospitalized, or to die (P <.05 for each outcome). These differences persisted and remained statistically significant when corrected for influenza immunization status. A total of 730 residents received oseltamivir prophylaxis for a median of 9 days (range 5-12). Of these, side effects were identified in 30 (4.1%), the most common being diarrhea (12 residents, 1.6%), cough (5, 0.7%), confusion (4, 0.5%) and nausea (4, 0.5%). CONCLUSIONS: Oseltamivir is safe and appears to be effective when used as treatment or prophylaxis to control outbreaks of influenza in older nursing home residents.

Acetamides↗
PubMed2000

Management of hospital outbreaks of gastro-enteritis due to small roundstructured viruses.

Small round structured viruses (SRSVs, Norwalk-like viruses, NLVs) are the most common cause of outbreaks of gastro-enteritis in hospitals and also cause outbreaks in other settings such as schools, hotels, nursing homes and cruise ships. Hospital outbreaks often lead to ward closure and major disruption in hospital activity. Outbreaks usually affect both patients and staff, sometimes with attack rates in excess of 50%. For this reason, staff shortages can be severe, particularly if several wards are involved at the same time. SRSVs may be spread by several routes: faecal-oral; vomiting/aerosols; food and water. Viruses may be introduced into the ward environment by any of these routes and then propagated by person-to-person spread. In an outbreak setting, the diagnosis can usually be made rapidly and confidently on clinical and epidemiological grounds, particularly if vomiting is a prominent symptom. By the time an SRSV outbreak has been recognized at ward level, most susceptible individuals will have been exposed to the virus and infection control efforts must prioritize the prevention of spread of infection to other clinical areas bycontainment of infected/exposed individuals (especially the prevention of patient and staff movements to other areas), hand-hygiene and effective environmental decontamination. This report of the Public Health Laboratory Service Viral Gastro-enteritis Working Group reviews the epidemiology of outbreaks of infection due to SRSVs and makes recommendations for their management in the hospital setting. The basic principles which underpin these recommendations will also be applicable to the management of some community-based institutional outbreaks.

Caliciviridae Infections↗
PubMed2001

Use of pulsed-field gel electrophoresis to investigate an outbreak of Serratia marcescens infection in a neonatal intensive care unit.

Serratia marcescens is a well-recognized hospital-acquired pathogen, which has been associated with a number of specific outbreaks, particularly in critically ill neonates. We used pulsed-field gel electrophoresis (PEGE) typing to analyse an outbreak in a neonatal intensive care unit (NICU). We included samples from nine patients, three handwashes and ten environmental isolates from an outbreak (February to August 1999) in addition to four patient isolates from different wards of our hospital during the same time period. The clinical presentations of the outbreak included bacteraemia (four cases), pneumonia (three cases), umbilical wound infection (one case) and conjunctivitis (one case). Nine outbreak isolates exhibited an identical PFGE fingerprint, while the epidemiologically unrelated strains demonstrated distinct patterns. Epidemiological investigation failed to reveal a common source of the outbreak, although the epidemic S. marcescens strain was isolated from hand-washes and doors of incubators. We concluded that cross-transmission via transient contamination of hands was the major route for this outbreak. Strict handwashing practices, the cohorting and isolation of colonized and infected patients, and the regular dis-infection of incubators are crucial steps for preventing the transmission of S. marcescens in an NICU. This PFGE method is highly discriminatory for the thorough epidemiological investigation of an outbreak of S. marcescens.

Cross Infection↗
PubMed2006

Modeling the role of bacteriophage in the control of cholera outbreaks.

Cholera is a waterborne diarrheal disease that continues to plague the developing world. Individuals become infected by consuming water from reservoirs contaminated by virulent strains of the bacterium Vibrio cholerae. Epidemiological and environmental observations of a cholera outbreak in Dhaka, Bangladesh, suggest that lytic bacteriophage specific for V. cholerae may limit the severity of cholera outbreaks by killing bacteria present in the reservoir and in infected individuals. To quantify this idea and generate testable hypotheses, we analyzed a mathematical model that combines the epidemiology of cholera with the population dynamics of the bacteria and phage. Under biologically reasonable conditions, we found that vibriophage can ameliorate cholera outbreaks. If phage predation limits bacterial density before an outbreak, a transient reduction in phage density can disrupt that limitation, and subsequent bacterial growth can initiate a cholera outbreak. The severity of the outbreak depends on the density of phage remaining in the reservoir. If the outbreak is initiated instead by a rise in bacterial density, the introduction of phage can reduce the severity of the outbreak and promote its decline. In both situations, the magnitude of the phage effect depends mainly on vibrio growth and phage mortality rates; the lower the rates, the greater the effect. Our analysis also suggests that either bacteria in the environmental reservoir are hyperinfectious or most victims ingest bacteria amplified in food or drinking water contaminated by environmental water carrying few viable V. cholerae. Our theoretical results make a number of empirically testable predictions.

Bacteriophages↗
PubMed2005

Outbreaks associated with recreational water in the United States.

In this article, we review the causes of outbreaks associated with recreational water during 1971-2000. A bacterial or protozoan etiology was identified in three-quarters of the outbreaks; 23% of the outbreaks were of undetermined etiology. The most frequently identified agents were Cryptosporidium (15%), Pseudomonas (14%), Shigella (13%), Naegleria (11%), Giardia (6%), and toxigenic E. coli (6%). Outbreaks attributed to Shigella, E. coli O157:H7, and Naegleria were primarily associated with swimming in fresh waters such as lakes, ponds, and rivers. In contrast, outbreaks caused by Cryptosporidium and Giardia were primarily associated with treated water in swimming and wading pools. Important sources of contamination for both treated and untreated recreational waters were the bathers themselves. Contamination from sewage discharges and wild or domestic animals were also important sources for untreated waters. Contributing factors in swimming-pool outbreaks were inadequate attention to maintenance, operation, disinfection, and filtration. Although not all waterborne outbreaks are recognized nor reported, the national surveillance of these outbreaks has helped identify important sources of contamination of recreational waters and the etiologic agents. This information can affect prevention recommendations and research priorities that may lead to improved water quality guidelines.

Animals↗
PubMed2000

Lack of immunity in university students before an outbreak of serogroup C meningococcal infection.

Immunity to meningococci was determined in infected and uninfected students before and during an outbreak of serogroup C meningococcal infection at a university in the United Kingdom. No immunity against the outbreak strain was detected in serum taken from infected students prior to the outbreak or at the time of admission; bactericidal activity developed during convalescence. Carriage of all strains of serogroup C meningococci in asymptomatic students was low (0.9%), and no carriage of the outbreak strain could be detected. Immunity in the at-risk student population before the outbreak was low: 90% of students had no significant bactericidal activity against the outbreak strain. A low prevalence of carriage of the outbreak strain, together with a low prevalence of protective immunity within the student population, was associated with a high incidence of invasive disease in those who acquired the outbreak strain.

Blood Bactericidal Activity↗
PubMed2004

Outbreaks of acute gastroenteritis on cruise ships and on land: identification of a predominant circulating strain of norovirus--United States, 2002.

In 2002, a sharp increase in outbreaks of norovirus-associated illness, both on cruise ships and on land, encouraged us to examine the molecular epidemiology of detected noroviruses, to identify a common strain or source. Of 14 laboratory-confirmed outbreaks on cruise ships, 12 (86%) were attributed to caliciviruses; among these 12, outbreak characteristics included continuation on successive cruises in 6 (50%), multiple modes of transmission in 7 (58%), and high (>10%) attack rates in 7 (58%). Eleven of the 12 calicivirus outbreaks were attributed to noroviruses, 7 (64%) of which were attributed to a previously unreported lineage, provisionally named "the Farmington Hills strain." From May 2002 to December 2002, 10 (45%) of 22 land-based outbreaks also were attributed to this strain. Nucleotide-sequence analysis provided insights into norovirus transmission, by documenting links among outbreaks, the introduction of strains onto ships, and viral persistence on board (despite cleaning). Control measures for outbreaks should address all routes of transmission. Better outbreak surveillance and collection of data on sequences will help to monitor norovirus strains and to identify common sources.

Acute Disease↗
PubMed2004

Detection and control of influenza outbreaks in well-vaccinated nursing home populations.

BACKGROUND: Influenza outbreaks continue to occur in nursing homes despite high vaccination coverage among residents. Recommendations for outbreak control in institutions such as nursing homes advises use of antiviral drugs to reduce influenza transmission. METHODS: Influenza surveillance was performed among elderly residents of nursing homes in Michigan during 2 influenza seasons. The antiviral drug oseltamivir was used for outbreak control at the discretion of nursing home staff once influenza transmission was confirmed by virus isolation or rapid antigen detection. RESULTS: During 2000-2001, influenza was not confirmed in any of the 28 participating homes, despite transmission of types A (H1N1) and B in the community. During 2001-2002, influenza type A (H3N2) transmission was confirmed in 8 (26%) of 31 participating homes; influenza vaccine coverage among residents was 57%- 98% in outbreak-associated homes. Oseltamivir was used in all homes with influenza transmission; outbreak control varied according to the rapidity of outbreak recognition and the extent of antiviral use. Reported adverse events were primarily gastrointestinal reactions and rashes. Analysis of the usefulness of rapid antigen detection tests for outbreak recognition indicated a sensitivity of only 77% (specificity, 92%). CONCLUSIONS: Oseltamivir was reasonably well tolerated, and its use, along with continued promotion of vaccination coverage among nursing home residents and staff, should be a valuable addition to institutional outbreak-control strategies.

Acetamides↗