Point-source Outbreak Research Articles

Diarrheal Outbreak Caused by Atypical EnteropathogenicEscherichia coliO157:H45 in South Korea

Background: In May 2013, an outbreak of gastroenteritis occurred in a high school in Incheon, South Korea. We investigated the outbreak in order to identify the pathogen and mode of transmission. A case-control study was performed using standardized questionnaires with a case definition of illness with diarrhea. Stool samples, environmental samples, and samples from preserved food items were collected to test pathogens. Pulsed-field gel electrophoresis (PFGE) was performed on the outbreak-related Escherichia coli strains. Thirty-three people (attack rate: 2.5%) met the case definition, and the pattern of the epidemic curve suggested a point-source outbreak. The common symptoms of cases were diarrhea (100.0%), abdominal pain (75.8%), chills (45.5%), and nausea (39.4%). Cases were found to be 8.26 times more likely to have eaten spicy fish soup with cod (95% confidence interval: 1.05-65.01). Consumption of egg soup with spring onions or braised eggs with razor clam flesh was significantly associated with illness. Atypical enteropathogenic E. coli O157:H45 was isolated from samples of 9 cases (27.3%) and tuna bibimbap. PFGE patterns of all tested isolates of O157 serotype were indistinguishable. This outbreak was caused by atypical enteropathogenic E. coli O157:H45 and the food vehicle was suspected to be tuna bibimbap. The statistical analysis was not in concordance with the microbiologic tests, probably owing to low pathogenicity of atypical enteropathogenic E. coli O157. This is the first report of an outbreak caused by atypical enteropathogenic E. coli O157.

Shiga toxin-producing E. coli (STEC) in swine: prevalence over the finishing period and characteristics of the STEC isolates.

This descriptive longitudinal study was conducted to investigate the faecal shedding of Shiga toxin-producing E. coli (STEC) in finishing swine and to characterize the swine STEC isolates that were recovered. Three cohorts of finishing swine (n = 50/cohort; total 150 pigs) were included in the longitudinal study. Individual faecal samples were collected every 2 weeks (8 collections/pig) from the beginning (pig age 10 weeks) to the end (pig age 24 weeks) of the finishing period. STEC isolates were recovered in at least one sample from 65·3% (98/150) of the pigs, and the frequency distribution of first-time STEC detection during the finishing period resembled a point-source outbreak curve. Nineteen O:H serotypes were identified among the STEC isolates. Most STEC isolates (n = 148) belonged to serotype O59:H21 and carried the stx 2e gene. One O49:H21 STEC isolate carried the stx 2e and eae genes. High prevalence rates of STEC during the finishing period were observed, and STEC isolates in various non-O157 serogroups were recovered. These data enhance understanding of swine STEC epidemiology, and future research is needed to confirm whether or not swine STEC are of public health concern.

Don't Count Your Chicken Livers: an Outbreak of Campylobacter sp. Not Associated with Chicken Liver Parfait, England, November 2013.

In England, several recent campylobacter outbreaks have been associated with poultry liver consumption. Following a lunch event in a hotel in Surrey in November 2013 where chicken liver parfait was served, guests reported having gastrointestinal symptoms. A retrospective cohort study showed 46 of 138 guests became unwell, with a median incubation period of two days and for 11 cases campylobacter infection was laboratory confirmed. Food item analysis identified an association between illness and consumption of roast turkey (aOR=3.02 p=0.041) or jus (aOR=3.55 p=0.045), but not with chicken liver parfait (OR=0.39 p=0.405). The environmental risk assessment did not identify non-compliance with standard food practice guidelines. This study presents a point-source outbreak of campylobacter with a high attack rate and epidemiological analysis results show that the jus or roast turkey was the likely source of infection although this could not be confirmed by the environmental assessment. Consuming the chicken liver dish was not a risk factor for developing symptoms as was initially hypothesised. Prior knowledge on the association between poultry liver food items and campylobacter outbreaks should not overly influence an outbreak investigation to ensure the true aetiology is identified and on-going public health risk is minimised.

Prolonged outbreak of Staphylococcus aureus surgical site infection traced to a healthcare worker with psoriasis

Meticillin-sensitive Staphylococcus aureus (MSSA) is a frequent cause of surgical site infection (SSI), but point-source outbreaks are rarely recognized. To describe an outbreak of MSSA SSI in a thoracic surgical unit. An outbreak investigation was started following two postoperative bacteraemias with MSSA resistant to fusidic acid (MSSA FusR). Patients with MSSA FusR were identified from microbiology records and through prospective case finding. Healthcare workers (HCWs) were screened. Isolates were characterized by phage typing, spa typing, pulsed-field gel electrophoresis and toxin gene profiling. A case-control study examined the association between one HCW with MSSA FusR and the patients involved in the outbreak. Nineteen patients were identified with MSSA FusR over 16 months. Four isolates were available for typing and all belonged to the same lineage. Seventy-six HCWs were screened. One was a carrier of the outbreak strain (a nurse with psoriasis). All 19 cases were exposed to this HCW compared with only 40/66 controls (P=0.003) and cases had a greater duration of exposure (P=0.00001, chi-squared for trend). Direct patient contact was documented in 15 cases. The outbreak was halted by thorough cleaning of the ward and removal of the HCW from clinical duty. The HCW with psoriasis was the source of this outbreak. MSSA FusR may be a marker for strains associated with skin conditions. HCWs with significant skin conditions may pose an infection risk in surgical settings. Recommendations are made for occupational health teams regarding screening of HCWs with dermatitis.

Linking time-varying symptomatology and intensity of infectiousness to patterns of norovirus transmission.

BackgroundNorovirus (NoV) transmission may be impacted by changes in symptom intensity. Sudden onset of vomiting, which may cause an initial period of hyper-infectiousness, often marks the beginning of symptoms. This is often followed by: a 1–3 day period of milder symptoms, environmental contamination following vomiting, and post-symptomatic shedding that may result in transmission at progressively lower rates. Existing models have not included time-varying infectiousness, though representing these features could add utility to models of NoV transmission.MethodsWe address this by comparing the fit of three models (Models 1–3) of NoV infection to household transmission data from a 2009 point-source outbreak of GII.12 norovirus in North Carolina. Model 1 is an SEIR compartmental model, modified to allow Gamma-distributed sojourn times in the latent and infectious classes, where symptomatic cases are uniformly infectious over time. Model 2 assumes infectiousness decays exponentially as a function of time since onset, while Model 3 is discontinuous, with a spike concentrating 50% of transmissibility at onset. We use Bayesian data augmentation techniques to estimate transmission parameters for each model, and compare their goodness of fit using qualitative and quantitative model comparison. We also assess the robustness of our findings to asymptomatic infections.ResultsWe find that Model 3 (initial spike in shedding) best explains the household transmission data, using both quantitative and qualitative model comparisons. We also show that these results are robust to the presence of asymptomatic infections.ConclusionsExplicitly representing explosive NoV infectiousness at onset should be considered when developing models and interventions to interrupt and prevent outbreaks of norovirus in the community. The methods presented here are generally applicable to the transmission of pathogens that exhibit large variation in transmissibility over an infection.

Gastroenteritis Outbreaks Caused by Norovirus Genotype II.7 in a College in China (Zhuhai, Guangdong) in 2011

Noroviruses are the most common cause of epidemic gastroenteritis worldwide. Noroviruses are comprised of at least five genogroups (GI-GV) and >35 genotypes. GII.7 is a nonpredominant genotype associated with Norovirus outbreaks. On November 17, 2011, Zhuhai Center for Disease Control monitored an increasing number of gastroenteritis cases at a local college. To determine the causes and control the outbreak effectively, we carried out an epidemiologic investigation. Suspected cases were defined as those with one of the following symptoms: nausea, vomiting, abdominal pain, or diarrhea presenting on or after November 15 among the people who lived at the college. Probable cases were defined as cases with vomiting or diarrhea over three times per day on or after November 15. Confirmed cases were suspected or probable cases positive for Norovirus (nucleic acid). We conducted a case-control study to identify risk factors of the outbreak. Norovirus was tested by real-time reverse transcription-polymerase chain reaction, and Norovirus polymerase chain reaction products were further sequenced. In total, 63 cases were identified, which were scattered in all 14 departments of the college. The outbreak lasted for 84 h. Time distribution mode indicated a point-source outbreak. Fifty-one cases and 94 controls were contacted. Seventy-five percent of the cases compared to 19% of the controls were exposed to delicatessens (various salad and meat products) from the "Y" convenience store (odds ratio=12, 95% confidence interval 5.4-28). Laboratory tests showed 14 of the 15 cases and two asymptomatic food handlers were positive for Norovirus nucleic acid. There was 100% similarity between the cases and the food handlers when we compared the nucleotide sequences of Norovirus, which clustered with GII.7 genotype. Delicatessens from the "Y" convenience store were associated with the GII.7 Norovirus outbreak. We strongly recommend food supervision and quality control in convenience stores to decrease the risk of future Norovirus outbreaks.

Syndromic surveillance for local outbreak detection and awareness: evaluating outbreak signals of acute gastroenteritis in telephone triage, web-based queries and over-the-counter pharmacy sales

For the purpose of developing a national system for outbreak surveillance, local outbreak signals were compared in three sources of syndromic data--telephone triage of acute gastroenteritis, web queries about symptoms of gastrointestinal illness, and over-the-counter (OTC) pharmacy sales of antidiarrhoeal medication. The data sources were compared against nine known waterborne and foodborne outbreaks in Sweden in 2007-2011. Outbreak signals were identified for the four largest outbreaks in the telephone triage data and the two largest outbreaks in the data on OTC sales of antidiarrhoeal medication. No signals could be identified in the data on web queries. The signal magnitude for the fourth largest outbreak indicated a tenfold larger outbreak than officially reported, supporting the use of telephone triage data for situational awareness. For the two largest outbreaks, telephone triage data on adult diarrhoea provided outbreak signals at an early stage, weeks and months in advance, respectively, potentially serving the purpose of early event detection. In conclusion, telephone triage data provided the most promising source for surveillance of point-source outbreaks.

A Norovirus Outbreak Related to Contaminated Surfaces

We investigated an outbreak of norovirus infection affecting 12 of 16 auto dealership employees (75%) subsequent to a staff meeting. Take-out sandwiches initially seemed the likely source, but a cohort study found no association between illness and food consumption. Employees reported seeing a toddler with diarrhea in a dealership restroom shortly before the luncheon. Indistinguishable norovirus was isolated from employees and the child (genotype GII6.C) and from a diaper-changing station in the restroom (genogroup GII). Counterintuitively, this point-source outbreak following a meal was caused by environmental exposures, not food. Environmental exposures should be considered even in routine outbreak investigations.

Syndromic Surveillance for Outbreak Detection and Investigation

For the purpose of developing a national system of outbreak surveillance, we compared local outbreak signals in three sources of syndromic data: telephone triage of acute gastroenteritis, web queries about symptoms of gastrointestinal illness, and OTC pharmacy sales of anti-diarrhea medication. The sensitivity and specificity were highest for telephone triage data. It provided the most promising source of syndromic data for surveillance of point-source outbreaks. Currently, a project has been initialized to develop and implement a national system in Sweden for daily syndromic surveillance based on 1177 Health Care Direct, supporting regional and local outbreak detection and investigation.

Epidemiological investigation of two parallel gastroenteritis outbreaks in school settings

BackgroundTwo parallel gastroenteritis outbreaks occurred in an elementary school and a neighboring kindergarten in Kilkis, Northern Greece in 2012. The aim of the study was the investigation of these two parallel outbreaks as well as their possible source.MethodsTwo retrospective cohort studies were performed to identify the mode and the vehicle of transmission as well as the possible connection between them.ResultsElementary school and kindergarten populations of 79.9% (119/149) and 51.1% (23/45) respectively, participated in the study. Case definition was satisfied by 65 pupils from the elementary school and 14 from the kindergarten. For elementary school, 53 cases were considered primary cases of the outbreak and were included in the analysis. Based on the results of the multivariate analysis, consumption of tap water was the only statistically significant independent risk factor of gastroenteritis (RR = 2.34, 95% C.I.: 1.55-3.53).; a finding supported by the shape of the epidemic curve which referred to a common point source outbreak with secondary cases. For kindergarten, no statistically significant risk factor was identified, and the epidemic curve supported a person-to-person transmission according univariate analysis. Norovirus GI and GII and human Adenovirus were detected by Real Time PCR in stool samples from seven children of elementary school, but stool samples were not collected by children of the kindergarten.ConclusionsEven though the etiological agent of the outbreak was not verified, combined epidemiological and laboratory results were in favor of a waterborne viral gastroenteritis outbreak at the elementary school, followed by a person to person spread at the kindergarten.

Cohort study of a dual-pathogen point source outbreak associated with the consumption of chicken liver pâté, UK, October 2009

In October 2009, a dual-pathogen outbreak of Campylobacter and Salmonella occurred in which 59 cases were identified among guests attending a regional conference in the North of England. The mean symptomatic period was 5.4 days ( confidence intervals: 4.4-6.4), and over 84% of the cases had abdominal pain and diarrhoea. A retrospective cohort study was used to investigate the outbreak, and active case-finding was performed through the conference organizers and environmental health officers. A focused questionnaire was distributed to all guests via the event organizers 10 days after the conference. Response rate among guests was 61% (107/175). A cohort study was undertaken, and a strong association was found between illness and consumption of chicken liver pâté, supporting the hypothesis that chicken liver pâté was the most likely cause of the outbreak. This is the first mixed pathogen outbreak documented associated with the consumption of chicken liver pâté and adds to the evidence of potential hazards associated with the undercooking of poultry livers. A rapid outbreak investigation with collaboration between several organizations and the venue led to identification of the most probable source.

A multistate epidemic outbreak of Salmonella Goldcoast infection in humans, June 2009 to March 2010: the investigation in Italy

After an urgent inquiry into a suspected international outbreak of Salmonella Goldcoast infection was launched by Hungary in October 2009 a nationwide multidisciplinary investigation was carried out in Italy. The aims were to verify whether the higher than expected number of cases of S. Goldcoast infection that had occurred in Italy in the previous months were linked to the outbreak in Hungary and to determine their origin. Between June 2009 and March 2010, 79 confirmed cases of S. Goldcoast infection were identified. Of these, 17 were part of three different point-source outbreaks probably associated with the consumption of salami. Eating salami was also reported by 20 of the 39 sporadic cases that could be interviewed. Fifteen strains of S. Goldcoast isolated from the cases were typed by pulsed-field gel electrophoresis. They shared more than 90% homology with the Hungarian epidemic strain and were also highly similar to S. Goldcoast strains that had been isolated in Italy from pigs and pork-containing food items in 2009 and 2010. Although the origin of the outbreak and the common source linking the Hungarian and the Italian cases could not be definitively identified, our results suggest a possible zoonotic connection of the outbreak cases with the pork production chain.

Microsporidial Keratoconjunctivitis Outbreak among Athletes from Hong Kong Who Visited Singapore, 2012

Microsporidial Keratoconjunctivitis Outbreak among Athletes from Hong Kong Who Visited Singapore, 2012

Listeriosis at a Tertiary Care Hospital in Beijing, China: High Prevalence of Nonclustered Healthcare-Associated Cases Among Adult Patients

Listeriosis is an emerging infectious disease associated with high mortality. There are few published reports from East Asia and developing countries. Our goal was to describe the clinical characteristics and outcomes of patients diagnosed with Listeria monocytogenes at a tertiary care hospital in Beijing, China. Peking Union Medical College Hospital (PUMCH), an 1800-bed hospital, consists of 2 campuses that house different medical departments. We retrospectively reviewed all culture-proven cases of listeriosis occurring at PUMCH between 1999 and 2011. Point estimates and 95% confidence intervals are presented. There were 38 patients with listeriosis: 5 neonatal, 8 maternal, and 25 nonmaternal. The median age of the adult nonmaternal patients was 47 (range, 18-79) years with a female predominance (72%). Forty percent (n = 10) had an underlying rheumatic disease. Forty-four percent of cases (n = 11) were healthcare-associated infections occurring a median of 20 (range, 3-44) days after hospital admission. Only 2 of the 11 healthcare-associated cases clustered in space and time. One healthcare-associated case occurred in a patient receiving KHI-272 therapy, an oral, irreversible dual EGFR/HER2 inhibitor. The neonatal and maternal listeriosis cases were similar to those reported in the literature. Nonclustered healthcare-associated cases of L. monocytogenes occurred at a large tertiary care hospital in Beijing, China. The source of these infections is unclear. Although rare, in the setting of immunosuppression, Listeria should be considered in the differential diagnosis of healthcare-associated infections, even in the absence of a point-source outbreak.

Nosocomial transmission of extensively drug-resistant tuberculosis in a rural hospital in South Africa.

Extensively drug-resistant tuberculosis (XDR-tuberculosis) is a global public health threat, but few data exist elucidating factors driving this epidemic. The initial XDR-tuberculosis report from South Africa suggested transmission is an important factor, but detailed epidemiologic and molecular analyses were not available for further characterization. We performed a retrospective, observational study among XDR-tuberculosis patients to identify hospital-associated epidemiologic links. We used spoligotyping, IS6110-based restriction fragment-length polymorphism analysis, and sequencing of resistance-determining regions to identify clusters. Social network analysis was used to construct transmission networks among genotypically clustered patients. Among 148 XDR-tuberculosis patients, 98% were infected with human immunodeficiency virus (HIV), and 59% had smear-positive tuberculosis. Nearly all (93%) were hospitalized while infectious with XDR-tuberculosis (median duration, 15 days; interquartile range: 10-25 days). Genotyping identified a predominant cluster comprising 96% of isolates. Epidemiologic links were identified for 82% of patients; social network analysis demonstrated multiple generations of transmission across a highly interconnected network. The XDR-tuberculosis epidemic in Tugela Ferry, South Africa, has been highly clonal. However, the epidemic is not the result of a point-source outbreak; rather, a high degree of interconnectedness allowed multiple generations of nosocomial transmission. Similar to the outbreaks of multidrug-resistant tuberculosis in the 1990s, poor infection control, delayed diagnosis, and a high HIV prevalence facilitated transmission. Important lessons from those outbreaks must be applied to stem further expansion of this epidemic.

When is an outbreak not an outbreak? Fit, divergent strains of Mycobacterium tuberculosis display independent evolution of drug resistance in a large London outbreak

To study the evolutionary relationship of Mycobacterium tuberculosis isolates from 13 patients in a large outbreak of isoniazid-resistant tuberculosis in London. Genotypic and phenotypic susceptibility tests were performed. Molecular genotyping using restriction fragment length polymorphisms and mycobacterial interspersed repetitive units was carried out. Additionally, the generation times of 13 strains of M. tuberculosis from the outbreak were measured to determine relative fitness. Genotypic and phenotypic susceptibility testing demonstrated variations between isolates. Polymorphisms causing isoniazid resistance varied within clusters of isolates that were indistinguishable by standard genotyping. The measurement of in vitro generation times demonstrated that the fitness of the resistant strains was not significantly different from either wild-type or susceptible isolates in the outbreak, indicating that apparently no fitness cost was associated with the acquisition of drug resistance. It appears that this outbreak comprised a heterogeneous collection of closely related strains, which appear to exhibit more variation than would usually be associated with a point source outbreak. These strains appear to have evolved by acquisition of additional antimicrobial resistance mutations while remaining competitive. The acquired resistance and retained competitiveness may be partly responsible for the difficulty in controlling the outbreak.

A large point-source outbreak of Salmonella Typhirium linked to chicken, pork and salad rolls from a Vietnamese bakery in Sydney

In January 2011, Sydney South West Public Health Unit was notified of a large number of people presenting with gastroenteritis over two days at a local hospital emergency department (ED). Case-finding was conducted through hospital EDs and general practitioners, which resulted in the notification of 154 possible cases, from which 83 outbreak cases were identified. Fifty-eight cases were interviewed about demographics, symptom profile and food histories. Stool samples were collected and submitted for analysis. An inspection was conducted at a Vietnamese bakery and food samples were collected and submitted for analysis. Further case ascertainment occurred to ensure control measures were successful. Of the 58 interviewed cases, the symptom profile included diarrhoea (100%), fever (79.3%) and vomiting (89.7%). Salmonella Typhimurium multiple-locus-variable number tandem repeats analysis (MLVA) type 3-10-8-9-523 was identified in 95.9% (47/49) of stool samples. Cases reported consuming chicken, pork or salad rolls from a single Vietnamese bakery. Environmental swabs detected widespread contamination with Salmonella at the premises. This was a large point-source outbreak associated with the consumption of Vietnamese-style pork, chicken and salad rolls. These foods have been responsible for significant outbreaks in the past. The typical ingredients of raw egg butter or mayonnaise and pate are often implicated, as are the food-handling practices in food outlets. This indicates the need for education in better food-handling practices, including the benefits of using safer products. Ongoing surveillance will monitor the success of new food regulations introduced in New South Wales during 2011 for improving food-handling practices and reducing foodborne illness.

An Outbreak of Mycoplasma pneumoniae Caused by a Macrolide-Resistant Isolate in a Nursery School in China

Eighteen out of 45 children were reported to have a respiratory illness during an outbreak at a temporary dormitory in a nursery school in China in 2011. To study the outbreak and to determine the risk factors for infection, an epidemiological investigation was performed. A standardized questionnaire was completed for a total of 45 children with the help of their guardians and parents. In addition, acute- and convalescent-phase serum samples and throat swabs from the children were taken for laboratory diagnosis. The diagnosis of a Mycoplasma-like illness was based on the following clinical criteria. The criteria were onset of illness after 31 May 2011, characterized by a cough, fever(>37.5 °C), or at least 3 of the following symptoms: fever, sore throat, cough or expectoration, and runny or stuffy nose. PCR-restriction fragment length polymorphism (PCR-RFLP), determination of MICs, and sequencing were performed to determine the genotype, antibiotic resistance, and sequence polymorphisms of the isolated strains, respectively. The paired sera revealed that 15 patients were infected with Mycoplasma pneumoniae. Epidemiology confirmed that this was a point source outbreak, characterized by a short incubation period, a high secondary attack rate, and a long period of hospitalization. PCR-RFLP analysis revealed that the 12 isolated strains of M. pneumoniae shared the same subtype P1 gene, and 23S rRNA sequence analysis showed that these strains harbored two macrolide-resistant gene-related point mutations at position 2063 and 2617. In this outbreak, the major risk factor was the distance between the bed of the first patient and the beds of close contacts (beds less than three meters apart). The strains isolated in this study were found to harbor two point mutations conferring macrolide resistance, indicating the importance of pathogen and drug resistance surveillance systems.

A Point-Source Norovirus Outbreak Caused by Exposure to Fomites

We investigated a norovirus outbreak (genotype GII.2) affecting 9 members of a soccer team. Illness was associated with touching a reusable grocery bag or consuming its packaged food contents (risk difference, 0.636; P<.01). By polymerase chain reaction, GII norovirus was recovered from the bag, which had been stored in a bathroom used before the outbreak by a person with norovirus-like illness. Airborne contamination of fomites can lead to subsequent point-source outbreaks. When feasible, we recommend dedicated bathrooms for sick persons and informing cleaning staff (professional or otherwise) about the need for adequate environmental sanitation of surfaces and fomites to prevent spread.

Rising incidence of Pneumocystis jirovecii pneumonia suggests iatrogenic exposure of immune-compromised patients may be becoming a significant problem

Against a background of point-source outbreaks of Pneumocystis pneumonia (PCP) in renal transplant units in Europe, we undertook a retrospective 3 year observational review of PCP in Northern Ireland. This showed an unexpected increase in incidence, with a mortality rate of 30 %. Fifty-one cases were confirmed compared to 10 cases confirmed in the preceding 7 years. Where undiagnosed HIV infection had previously been the main risk factor for PCP, this was now equally matched by chemotherapy for haematological and non-haematological malignancy and immune suppression for a range of autoimmune conditions. Congenital immunodeficiency and transplantation were less common predisposing factors, but renal grafts also showed a rising incidence. Asymptomatic carriage was uncommon. At presentation both upper and lower respiratory samples were of equal use in establishing the diagnosis, and treatment resulted in rapid clearance. These data suggest the need for considering PCP in at-risk patients, reviewing its mode of acquisition and whether iatrogenic colonization is a treatable pre-condition.