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PubMed1995

Outbreak of cryptosporidiosis associated with a disinfected groundwater supply.

In an outbreak of cryptosporidiosis in Warrington, a town in North-West England, 47 cases were recorded between November 1992 and February 1993, most within the first month. There was a strong statistical association between cases and residence in an area supplied from two groundwater sources. In a case-control study, a strong association between having drunk unboiled tap water from these sources, and a dose-response relationship were found. Oocysts were not detected in the water supply. During very heavy rainfall one source of water was found to drain surface water directly from a field containing livestock faeces, thereby bypassing natural sandstone filtration. Exceptionally heavy rainfall occurred at the probable time of infection. After withdrawal of the original water supply, the outbreak rapidly subsided. It was concluded that there was very strong evidence that this outbreak was waterborne. This, the second documented outbreak of cryptosporidiosis attributable to a groundwater supply, demonstrates that infection can be transmitted from a disinfected groundwater source despite apparently satisfactory treated water quality. We recommended that guidelines for protection of groundwater are implemented, raw groundwater should be routinely monitored for microbiological contamination, and the structure of all sources and waterworks should be assessed in risk surveys of water catchment areas.

Adult↗

PubMed2002

Molecular subtyping of Staphylococcus aureus from an outbreak associated with a food handler.

On 6 May 2000, a staphylococcal food poisoning outbreak occurred at a high school, affecting 10 of the 356 students who attended the breakfast. Twenty-seven Staphylococcus aureus isolates, producing enterotoxin A (SEA), SEB-, or non-SEA-E, were recovered from 7 patients, 2 food handlers and left-overs. To investigate the outbreak, we genotyped the isolates by using pulsed-field gel electrophoresis (PFGE) and three PCR-based techniques: inter-IS256 PCR typing, protein A gene (spa) typing, and coagulase gene restriction profile (CRP) analysis. Our results show that PFGE was the most discriminatory technique, whereas the three PCR-based techniques were insufficient in the discriminatory power to distinguish the S. aureus isolates from the outbreak. Based on the enterotoxin-producing types and the results of genotyping, three distinct types of strains (A1111, B2221 and N3221) were designated. Both the A1111 and B2221 strains were found in the specimens from the patients and a hand lesion of a food handler, suggesting that the source of contamination for the outbreak was most likely originated from a food handler.

Adolescent↗

PubMed2002

A large hotel outbreak of Norwalk-like virus gastroenteritis among three groups of guests and hotel employees in Virginia.

A large outbreak of acute gastroenteritis occurred among three different groups of guests and the employees of a Virginia hotel within a 2-week period in November 2000. At least 76 of the hotel's guests and 40 hotel employees had acute gastroenteritis during this period. All tested ill persons were infected with the same strain of Norwalk-like virus, as shown by cloning and sequencing of virus detected in stool specimens from the three guest groups and the employees. Epidemiologic investigation suggested food as the probable source for the guests. Most of the employees, including those sick, did not eat in the hotel, suggesting that environmental contamination and person-to-person transmission could have contributed to the outbreak. The disease continued to spread in the hotel, passing from one guest group to another, by food, environmental contamination, and/or by person-to-person transmission through infected employees and guests. The study describes procedures implemented to control the outbreak and makes recommendations for future outbreak control.

Adult↗

PubMed2002

A prolonged outbreak of Norwalk-like calicivirus (NLV) gastroenteritis in a rehabilitation centre due to environmental contamination.

An outbreak of Norwalk-like calicivirus (NLV) gastroenteritis occurred in a rehabilitation centre in southern Finland between December 1999 and February 2000. An epidemiological investigation was conducted to determine the source and extent of the outbreak. More than 300 guests and staff members became ill during the outbreak. No food or activity in the centre could be linked epidemiologically to illness. NLV genogroup II was detected by RT-PCR in stool samples of symptomatic guests and employees. All strains reacted similarly with the microplate hybridization probe panel and showed the same nucleotide sequence, indicating that they represented the same NLV strain. Food and water samples were negative for NLV, whereas NLV was detected in three environmental specimens. The strains from patients and environment were identical based on microplate hybridization probes, suggesting that environmental contamination may have been important for the spread of calicivirus and the protracted course of the outbreak.

Adult↗

PubMed2003

The use of the case-crossover design in a continuous common source food-borne outbreak.

When applicable, case-crossover studies may be quicker and cheaper to complete than case-control studies. Because time is a major issue in outbreak investigations, we evaluated the interest of this design during a continuous common source food-borne outbreak of salmonellosis for which the vehicle (hamburgers) was also implicated by environmental and laboratory investigations. Seventeen of the 35 cases identified in the outbreak were included in the study according to the availability of menu records with detailed information on food consumed at each meal. Food exposures during a 3-day risk period before onset of illness were compared to those of a control time-interval of the same duration that preceded the risk period by two days. Seventy-seven per cent of the cases (13/17) had consumed hamburgers in the three days preceding onset of illness compared with 29% (5/17) during the control period (P = 0.04, odds ratio = 5, 95% CI: 1.1-46.9). In this investigation the case-crossover design proved to be a useful and efficient alternative to the case-control approach. However, further evaluation of this design in outbreak investigation is needed.

Adolescent↗

PubMed2004

E-mail surveys assist investigation and response: a university conjunctivitis outbreak.

A conjunctivitis outbreak affecting more than 200 individuals occurred on a university campus in Evanston, Illinois, USA, in spring 2002. An investigation was conducted jointly by the Evanston Department of Health and the Illinois Department of Public Health. A combination of e-mail and traditional telephone-based surveys demonstrated that wearing contact lenses was a risk factor for any conjunctivitis and bilateral conjunctivitis, whereas using glasses was protective. Laboratory and epidemiological evidence suggested that the outbreak was caused by a viral pathogen that eluded characterization despite extensive culture and PCR-based laboratory testing. Enhanced laboratory surveillance could help clinicians and public-health officials to identify relevant secular changes in the spectrum of causes of conjunctivitis. During institutional outbreaks, e-mail surveys can help public-health officials to efficiently access information not easily collected by traditional case-control studies, and can provide an effective conduit for providing prevention recommendation, such as the need for improved hand and contact-lens hygiene during outbreaks.

Adult↗

PubMed2004

Salmonella Enteritidis outbreak associated with a school-lunch dessert: cross-contamination and a long incubation period, Japan, 2001.

A Salmonella Enteritidis (SE) outbreak in Japan was investigated with an observational study, analytical epidemiology and bacteriological examination (including phage typing). The outbreak occurred among 96 schoolchildren, and was caused by SE phage type 1. The outbreak source was dessert buns served at a school lunch (RR 42.55, 95 % CI 5.93-305.11, P < 0.001). The buns were probably cross-contaminated from eggs from a factory with a history of SE-contaminated products. The incubation period was longer than usual (3-16 days, median 8 days). A low contaminating dose may account for the long incubation period and low attack rate. Outbreak detection was hampered by the absence of routine Salmonella surveillance in Japan. The investigation was complicated by concurrent illnesses from other SE phage types. It was successful, in part, because adequate food samples were available for microbiological testing.

Child↗

PubMed2005

A large-scale gastroenteritis outbreak associated with Norovirus in nursing homes.

An increase in gastroenteritis outbreaks due to Norovirus has been reported worldwide. We investigated a large-scale outbreak affecting 246 residents and 33 staff members in six nursing homes in the Tel-Aviv district, Israel, during 3 weeks in 2002. Person-to-person spread was noticed in all nursing homes. The spread of disease could not be attributed to social interactions. Among the elderly residents, the hospitalization rate was 10.2% and the case-fatality rate was 2.0%. Bacteriological cultures were negative. Overall, 7 out of 15 stool specimens were positive for Norovirus by RT-PCR. All were sequenced and found to be 90% identical. The characteristics of this outbreak and the RT-PCR results suggest that illness was caused by Norovirus. Due to the high case-fatality rate of Norovirus gastroenteritis, there should be a high index of suspicion when encountering a gastroenteritis outbreak among the elderly. This will enable prompt action to stop the spread of illness.

Adult↗

PubMed2005

Outbreaks of gastroenteritis due to infections with Norovirus in Switzerland, 2001-2003.

Viral infections, especially those with noroviruses are the most common cause of acute gastroenteritis in Europe. To obtain information about the epidemic situation of noroviruses in Switzerland, an initial study was launched in the German-speaking part of the country to systematically compile Norovirus outbreak information between 2001 and 2003. In total, 73 outbreaks were registered. Most affected were closed settings, e.g. nursing homes (34%) and hospitals (25%). Transmission pathways were identified in 74% of Norovirus outbreaks. In 81% of these cases person-to-person transmission was the primary route of infection and on seven occasions (13%), a foodborne transmission was the possible cause. Furthermore, Norovirus outbreak characteristics of epidemiological importance are highlighted with a discussion of four selected events.

Caliciviridae Infections↗

PubMed2005

A multi-state outbreak of Salmonella serotype Thompson infection from commercially distributed bread contaminated by an ill food handler.

Foodborne transmission is estimated to account for 95% of non-typhoidal Salmonella infections reported in the United States; however, outbreaks of salmonellosis are rarely traced to food handlers. In August 2000, an increase in Salmonella serotype Thompson infection was noted in Southern California; most of the cases reported eating at a restaurant chain (Chain A) before illness onset. A case-control study implicated the consumption of burgers at Chain A restaurants. The earliest onset of illness was in a burger bun packer at Bakery B who had not eaten at Chain A but had worked while ill. Bakery B supplied burger buns to some Chain A restaurants in Southern California and Arizona. This outbreak is notable for implicating a food handler as the source of food contamination and for involving bread, a very unusual outbreak vehicle for Salmonella . Inadequate food-handler training as well as delayed reporting to the health department contributed to this outbreak.

Adolescent↗

PubMed2005

Foodborne general outbreaks of Shiga toxin-producing Escherichia coli O157 in England and Wales 1992-2002: where are the risks?

Between 1 January 1992 and 31 December 2002, Shiga toxin-producing Escherichia coli O157 (STEC O157) accounted for 44 of the 1645 foodborne general outbreaks of infectious intestinal disease reported to the Health Protection Agency Communicable Disease Surveillance Centre. These outbreaks, although rare, were characterized by severe infection, with 169 hospital admissions and five deaths reported. STEC O157 outbreaks were compared with other pathogens to identify factors associated with this pathogen. Single risk variable analysis and logistic regression were employed. Two distinct aetiologies were identified. Foodborne outbreaks of STEC O157 infection in England and Wales were independently associated with farms, which related to milk and milk products, and with red meats/meat products, which highlighted butchers' shops as a cause for concern. The introduction and adherence to effective control measures, based on the principles of hazard analysis, provide the best means of minimizing the risk of foodborne infection with this pathogen.

Disease Outbreaks↗

PubMed2006

An outbreak of Cryptosporidium hominis infection at an Illinois recreational waterpark.

Cryptosporidium has become increasingly recognized as a pathogen responsible for outbreaks of diarrhoeal illness in both immunocompetent and immunocompromised persons. In August 2001, an Illinois hospital reported a cryptosporidiosis cluster potentially linked to a local waterpark. There were 358 case-patients identified. We conducted community-based and waterpark-based case-control studies to examine potential sources of the outbreak. We collected stool specimens from ill persons and pool water samples for microscopy and molecular analysis. Laboratory-confirmed case-patients (n=77) were more likely to have attended the waterpark [odds ratio (OR) 16.0, 95% confidence interval (CI) 3.8-66.8], had pool water in the mouth (OR 6.0, 95% CI 1.3-26.8), and swallowed pool water (OR 4.5, 95% CI 1.5-13.3) than age-matched controls. Cryptosporidium was found in stool specimens and pool water samples. The chlorine resistance of oocysts, frequent swimming exposures, high bather densities, heavy usage by diaper-aged children, and increased recognition and reporting of outbreaks are likely to have contributed to the increasing trend in number of swimming pool-associated outbreaks of cryptosporidiosis. Recommendations for disease prevention include alteration of pool design to separate toddler pool filtration systems from other pools. Implementation of education programmes could reduce the risk of faecal contamination and disease transmission.

Adolescent↗

PubMed2006

A recurring outbreak of Shigella sonnei among traditionally observant Jewish children in New York City: the risks of daycare and household transmission.

Dispersed community outbreaks of Shigella sonnei have occurred cyclically among traditionally observant Jews in the United States. In February 2000, we investigated a S. sonnei outbreak in one Jewish community in New York City. To determine risk factors for introduction of infection into households, we conducted a cohort study of households to compare risk factors for illness among primary subjects within households and age-matched well siblings. Isolates were subtyped by pulsed-field gel electrophoresis (PFGE). We used a random effects model to assess extra-household vs. intra-household transmission in households with multiple ill household members. Daycare or pre-school attendance [matched odds ratio (mOR) 16.1, P<0.001] and age <60 months (mOR 6.3, P<0.001) were independently associated with index subject illness. Outbreak isolates were closely related by PFGE analysis to the strain previously observed in Jewish community outbreaks. The random effects model strongly indicated that multiple illnesses in a single household are due to secondary transmission. Disease containment efforts should focus on reducing Shigella transmission in childcare settings and within homes.

Case-Control Studies↗

PubMed2006

Discernment between deliberate and natural infectious disease outbreaks.

Public health authorities should be vigilant to the potential for outbreaks deliberately caused by biological agents (bioterrorism). Such events require a rapid response and incorporation of non-traditional partners for disease investigation and outbreak control. The astute application of infectious disease epidemiological principles can promote an enhanced index of suspicion for such events. We discuss epidemiological indicators that should be considered during outbreak investigations, and also examine their application during bioterrorism incidents, an accidental release of an agent, outbreaks of infections that were alleged to have been deliberately initiated, and a model scenario. The Grunow & Finke epidemiological assessment tool is used to examine these historical events and the model scenario. The results received from this analysis, coupled with an understanding of epidemiological clues to unnatural events, and knowledge of how to manage such events, can aid in the improved response and resolution of epidemics.

Anthrax↗

PubMed1998

National outbreak of Salmonella senftenberg associated with infant food.

Eight cases of Salmonella senftenberg infection in infants were identified in the first half of 1995 in England, five were indistinguishable S. senftenberg strains. A case-control study showed an association between illness and consumption of one brand of baby cereal (P = 0.03). The cereal manufacturer reported isolating S. senftenberg in June 1994 from an undistributed cereal batch. Outbreak strains and the cereal strain were all plasmid-free in contrast to other human isolates of S. senftenberg in the same period. Changes in the production process were implemented to prevent further contamination. Surveillance centres should strengthen the detection and investigation of outbreaks of gastrointestinal infection in susceptible groups, especially young children. In this outbreak, the study of only five cases led to identification of the vehicle of infection. Even when few cases are reported, epidemiological investigation in conjunction with molecular typing may lead to public health action which prevents continuing or future outbreaks.

Case-Control Studies↗

PubMed1998

A campylobacter outbreak associated with stir-fried food.

An outbreak of gastrointestinal illness affecting 12 of 29 customers of a 'Hawaiian' theme restaurant specializing in stir-fried food occurred in Cardiff, Wales in February 1997. Campylobacter jejuni serotype HS50 phage type 49 (PT49) was isolated from 5 cases. A total of 47 isolates of C. jejuni HS50 PT49 were identified from Wales during 1997, of which 11 were isolated in late February or early March and from the Cardiff area. In the outbreak, illness was associated with eating stir-fried chicken pieces (relative risk 4.81, 95% confidence interval (CI) 0.76-30.44, P=0.03) and a dose-response relationship between risk of illness and amount of chicken consumed was observed (chi2-test for linear trend 3.96, P=0.047). Undercooking of chicken was probably due to a combination of inadequate cooking time and use of large chicken pieces. This is the first time that stir-fried food has been associated with a campylobacter outbreak. The incident also illustrates the value of routine campylobacter subtyping in supporting outbreak investigation.

Campylobacter Infections↗

PubMed1998

A community outbreak of invasive and non-invasive group A beta-haemolytic streptococcal disease in a town in South Wales.

An increase in the incidence of invasive and non-invasive infections caused by group A beta-haemolytic streptococci (GAS) was noted in and around the town of Glynneath (population approx. 4000) in West Glamorgan, South Wales between 1 January and 30 June 1995. A total of 133 cases was ascertained with 127 (96%) occurring between 1 March and 30 June 1995. Six patients had invasive disease (one died) and all presented at the peak of the outbreak. There were 127 non-invasive cases of whom 7 were hospitalized. The outbreak was investigated to determine its extent and whether it was caused by a single M-serotype of GAS. Serotyping showed that 13 different M-serotypes were involved with the M1 serotype predominating. The overall incidence of GAS invasive disease in West Glamorgan (population 365,000) increased sevenfold from a crude incidence of 0.5/10(5) per year in 1994 to 3.5/10(5) per year in 1995, but fell back to 0.75/10(5) per year in 1996. Eighty-two (80%) out of 102 individuals affected by GAS replied to a health questionnaire; sore throat was the commonest symptom reported (97%). Thirty-nine of these index cases identified at least one other member of their household who had experienced similar symptoms. The interval between the onset of illness in members of a single household was 0-83 days with a mean of 22 days. The mean duration of illness was 13.5 days and 61% of patients were treated with penicillin V for a mean duration of 9.3 days. Twenty-one per cent of GAS isolates were erythromycin-resistant and the M4 and M6 serotypes were especially resistant to erythromycin (87.5 and 100% resistance, respectively). Penicillin V failed to eradicate GAS from the throats of 25% of assessable patients. In this community, an outbreak of non-invasive disease caused by GAS was linked in time and place with an outbreak of serious invasive disease.

Adolescent↗

PubMed1999

A community outbreak of food-borne small round-structured virus gastroenteritis caused by a contaminated water supply.

In August 1994, 30 of 135 (23%) bakery plant employees and over 100 people from South Wales and Bristol in the United Kingdom, were affected by an outbreak of gastroenteritis. Epidemiological studies of employees and three community clusters found illness in employees to be associated with drinking cold water at the bakery (relative risk 3.3, 95%, CI 1.6-7.0), and in community cases with eating custard slices (relative risk 19.8, 95%, CI 2.9-135.1) from a variety of stores supplied by one particular bakery. Small round-structured viruses (SRSV) were identified in stool specimens from 4 employees and 7 community cases. Analysis of the polymerase and capsid regions of the SRSV genome by reverse transcription-polymerase chain reaction (RT-PCR) demonstrated viruses of both genogroups (1 and 2) each with several different nucleotide sequences. The heterogeneity of the viruses identified in the outbreak suggests that dried custard mix may have been inadvertently reconstituted with contaminated water. The incident shows how secondary food contamination can cause wide-scale community gastroenteritis outbreaks, and demonstrates the ability of molecular techniques to support classical epidemiological methods in outbreak investigations.

Adolescent↗