Outbreak of Neisseria meningitidis C in workers at a large food-processing plant in Brazil: challenges of controlling disease spread to the larger community

SUMMARYAn outbreak of meningococcal disease (MD) with severe morbidity and mortality was investigated in midwestern Brazil in order to identify control measures. A MD case was defined as isolation of Neisseria meningitidis, or detection of polysaccharide antigen in a sterile site, or presence of clinical purpura fulminans, or an epidemiological link with a laboratory-confirmed case-patient, between June and August 2008. In 8 out of 16 MD cases studied, serogroup C ST103 complex was identified. Five (31%) cases had neurological findings and five (31%) died. The attack rate was 12 cases/100 000 town residents and 60 cases/100 000 employees in a large local food-processing plant. We conducted a matched case-control study of eight primary laboratory-confirmed cases (1:4). Factors associated with illness in single variable analysis were work at the processing plant [matched odds ratio (mOR) 22, 95% confidence interval (CI) 2·3-207·7, P<0·01], and residing <1 year in Rio Verde (mOR 7, 95% CI 1·11-43·9, P<0·02). Mass vaccination (>10 000 plant employees) stopped propagation in the plant, but not in the larger community.     

An outbreak of viral meningitis associated with a public swimming pond

From July to October 2001, 215 cases of aseptic meningitis occurred among the inhabitants of the German city of Kassel and neighbouring counties. A matched case-control study identified bathing in a public, nature-like pond during the beginning of the outbreak as a risk factor for disease [matched odds ratio (mOR) 44.8, 95% confidence interval (CI) 3.9-515.6]. Among bathers, patients with meningitis spent more time in the water (mOR 18.8, 95% CI 2.0-174.1) and swallowed water more frequently (mOR = 7.3, 95% CI 0.7-81.8). Of 30 cerebrospinal fluid samples tested, echovirus 30 was cultured from 16, and echovirus 13 from seven. An echovirus 30 sequence obtained from one pond water sample showed a 99% nucleotide and 100% amino-acid homology with patient isolates. This outbreak demonstrates the potential of nature-like swimming ponds to cause widespread community infection with substantial public health impact.     

Salmonella enterica serovar Agona European outbreak associated with a food company

We investigated an international outbreak of Salmonella Agona with a distinct PFGE pattern associated with an Irish Food company (company X) producing pre-cooked meat products sold in various food outlet chains in Europe. The outbreak was first detected in Ireland. We undertook national and international case-finding, food traceback and microbiological investigation of human, food and environmental samples. We undertook a matched case-control study on Irish cases. In total, 163 cases in seven European countries were laboratory-confirmed. Consumption of food from food outlet chains supplied by company X was significantly associated with being a confirmed case (mOR 18·3, 95% CI 2·2-149·2) in the case-control study. The outbreak strain was isolated from the company's pre-cooked meat products and production premises. Sufficient evidence was gathered to infer the vehicles of infection and sources of the outbreak and to justify the control measures taken, which were plant closure and food recall.     

An incident case-control study of modes of hepatitis C virus transmission in France

PURPOSE: Risk factors for hepatitis C virus (HCV) infection have rarely been estimated using incident case-control studies in the "general" population. We undertook a case-control study of incident HCV infection to identify persistent modes of transmission in France. METHODS: Two types of case-patients were included: (1) repeat blood donors who seroconverted between 1998 and 2001 (with a last negative third-generation test reported from 1995 or after) and (2) seroconverters referred to hepatology departments in 2000 through 2001. For each case-patient, four age- and sex-matched controls were randomly selected from the population of occurrence. Data on risk factors were recorded for each case-patient's and matched control's referent exposure period (between last negative and first positive tests). RESULTS: Sixty-four case-patients and 227 controls were included. In univariate analysis, endoscopy (matched odds ratios [mORs] = 8.0; 95% confidence intervals [CI] = 2.3-27.2), general anesthesia (mOR = 5.6; 95% CI = 2.2-14.7), tattooing or body piercing (mOR = 8.8; 95% CI = 1.7-44.1), and intravenous (IV) drug use (p < 0.0001; mOR not defined) were associated with HCV seroconversion. In multivariate analysis, risk factors associated with HCV seroconversion were drug use (adjusted OR [aOR] = 109.0; 95% CI = 11.7-1015.8), digestive endoscopy (aOR = 5.7; CI = 1.4-23.8), and invasive radiology procedures (aOR = 11.6; CI = 1.7-78.5). CONCLUSIONS: The results showed the continuing major role of IV drug use and suggested that transmission related to invasive health care remained a potential source of new HCV infection between 1995 and 2001.     

Multistate outbreak of Salmonella serotype Typhimurium infections associated with consumption of restaurant tomatoes, USA, 2006: hypothesis generation through case exposures in multiple restaurant clusters

SUMMARY Multiple salmonellosis outbreaks have been linked to contaminated tomatoes. We investigated a multistate outbreak of Salmonella Typhimurium infections among 190 cases. For hypothesis generation, review of patients' food histories from four restaurant-associated clusters in four states revealed that large tomatoes were the only common food consumed by patients. Two case-control studies were conducted to identify food exposures associated with infections. In a study conducted in nine states illness was significantly associated with eating raw, large, round tomatoes in a restaurant [matched odds ratio (mOR) 3·1, 95% confidence interval (CI) 1·3-7·3]. In a Minnesota study, illness was associated with tomatoes eaten at a restaurant (OR 6·3, mid-P 95% CI 1·05-50·4, P=0·046). State, local and federal regulatory officials traced the source of tomatoes to Ohio tomato fields, a growing area not previously identified in past tomato-associated outbreaks. Because tomatoes are commonly eaten raw, prevention of tomato contamination should include interventions on the farm, during packing, and at restaurants.     

Investigation of a large community-based outbreak of hepatitis B infection in the United Kingdom

We describe the largest outbreak of hepatitis B virus infection reported to date in the UK. Between July 2001 and December 2005, 237 cases were identified in Avon, South West England. The likely route of transmission was injecting drug use in 44% (104/237) and heterosexual intercourse in 30% (71/237) of cases. A case-control study in injectors showed that injecting crack cocaine [adjusted odds ratio (aOR) 23·8, 95% confidence interval (CI) 3·04-186, P<0·001] and sharing injecting paraphernalia in the year before diagnosis (aOR 16·67, 95% CI 1·78-100, P=0·010) were strongly associated with acute hepatitis B. In non-IDUs number of sexual partners and lack of consistent condom use were high compared to a national sample. We describe the control measures implemented in response to the outbreak. This outbreak has highlighted the problems associated with the low uptake from the national hepatitis B vaccination policy which targets high-risk groups, the difficulties of identifying those at risk of acquiring hepatitis B infection through heterosexual sex, and injecting crack cocaine as a risk factor for hepatitis B.     

Gastroenteritis in older people living in the community: results of two Australian surveys

SUMMARY We analysed two large national surveys conducted in 2001 and 2008 to examine incidence and outcomes of gastroenteritis in older Australians. A case was someone reporting ?3 loose stools or ?1 episode of vomiting in 24 h, excluding non-infectious causes. We compared cases arising in the elderly (?65 years) and in other adults (20-64 years). Elderly people experienced 0·33 [95% confidence interval (CI) 0·24-0·42] episodes of gastroenteritis/person per year, compared to 0·95 (95% CI 0·74-1·15) in other adults. Elderly cases reported less stomach cramps, fever and myalgia than younger cases, and were more likely to be hospitalized, although this was not statistically significant. In multivariable analysis, gastroenteritis in elderly people was associated with travelling within the state (odds ratio 1·35, 95% CI 1·07-1·71). Elderly people were less concerned about food safety than other adults. Older Australians were less likely to report gastroenteritis and experienced different symptoms and outcomes from other adults.     

Mycobacterium massiliense outbreak after intramuscular injection, South Korea

SUMMARY We conducted an epidemic investigation to discover the route of transmission and the host factors of an outbreak of post-injection abscesses. Of the 2984 patients who visited a single clinic, 77 cases were identified and 208 age- and sex-matched controls were selected for analysis. Injected medications per se were not found to be responsible, and a deviation from safe injection practice suggested the likelihood of diluent contamination. Therefore the injected medications were classified according to whether there was a need for a diluent, and two medications showed a statistically significant association, i.e. injection with pheniramine [adjusted odds ratios (aOR) 5·93, 95% confidence interval (CI) 2·97-11·87] and ribostamycin (aOR 47·95, 95% CI 11·08-207·53). However, when considered concurrently, pheniramine lost statistical significance (aOR 8·71, 95% CI 0·44-171·61) suggesting that normal saline was the causative agent of this outbreak. Epidemiological evidence strongly suggested that this post-injection outbreak was caused by saline contaminated with Mycobacterium massiliense without direct microbiological evidence.     

Frozen chicken nuggets and strips and eggs are leading risk factors for Salmonella Heidelberg infections in Canada

A case-control study was conducted from 1 January to 31 May 2003 to identify risk factors for S . Heidelberg infection in Canada. Controls were pair-matched by age group and telephone exchange to 95 cases. Exposures in the 7 days before illness/interview were assessed using multivariate conditional logistic regression. Consumption of home-prepared chicken nuggets and/or strips [matched odds ratio (mOR) 4.0, 95% confidence interval (CI) 1.4-13.8], and undercooked eggs (mOR 7.5, 95% CI 1.5-75.5) increased the risk of illness. Exposure to a farm setting lowered the risk (mOR 0.22, 95% CI 0.03-1.00). The population-attributable fraction associated with chicken nuggets/strips was 34% and with undercooked eggs was 16%. One-third of study participants did not perceive, handle or prepare chicken nuggets and strips as high-risk products, although the majority of the products on the Canadian market are raw. These findings have prompted changes in product-labelling policy and consumer education.     

Shigellosis outbreak linked to canteen-food consumption in a public institution: a matched case-control study

On 13 November 2009, the authorities of Flemish Brabant, Belgium, received an alert concerning a potential outbreak of Shigella sonnei at a public institution. A study was conducted to assess the extent, discover the source and to implement further measures. We performed a matched case-control study to test an association between shigellosis and canteen-food consumption. Water samples and food handlers' faecal samples were tested. The reference laboratory characterized the retrospectively collected Shigella specimens. We found 52 cases distributed over space (25/35 departments) and time (2 months). We found a matched odds ratio of 3·84 (95% confidence interval 1·02-14·44) for canteen-food consumption. A food handler had travelled to Morocco shortly before detection of the first laboratory-confirmed case. Water samples and food handlers' faecal samples tested negative for Shigella. Confirmed cases presented PFGE profiles, highly similar to archived isolates from Morocco. Foodborne transmission associated with the canteen was strongly suspected.     

Estimating influenza vaccine effectiveness in an outbreak when anti-viral medications were used as a control measure

OBJECTIVES: To estimate influenza vaccine effectiveness (VE) from an outbreak of influenza A in an aged care facility in which neuraminidase inhibitors were used as part of outbreak control measures. METHODS: The outbreak occurred between 25 December 2001 and 21 January 2002. Neuraminidase inhibitors were used to control the outbreak. Residents and staff with respiratory symptoms were tested for influenza using RT-PCR and/or serology. Vaccine effectiveness (VE) was estimated for the prevention of laboratory-confirmed influenza. RESULTS: Nineteen of 42 (45%) residents and four of 29 (14%) staff were laboratory-confirmed as cases. The outbreak was caused by an influenza A (H3N2) strain, antigenically matched to that season's vaccine. The VE for preventing laboratory-confirmed influenza infection was 61% (95% CI 41-73) among residents and 100% (95% CI 63-100) among staff. CONCLUSIONS: The VE estimates calculated from this outbreak were consistent with other published results. Outbreaks of influenza in institutions provide a good opportunity to review influenza VE, but use of antiviral medications as control measures may affect interpretation of findings.     

A cholera outbreak among semi-nomadic pastoralists in northeastern Uganda: epidemiology and interventions

In sub-Saharan Africa, many nomadic pastoralists have begun to settle in permanent communities as a result of long-term water, food, and civil insecurity. Little is known about the epidemiology of cholera in these emerging semi-nomadic populations. We report the results of a case-control study conducted during a cholera outbreak among semi-nomadic pastoralists in the Karamoja sub-region of northeastern Uganda in 2010. Data from 99 cases and 99 controls were analysed. In multivariate analyses, risk factors identified were: residing in the same household as another cholera case [adjusted odds ratio (aOR) 6·67, 95% confidence interval (CI) 2·83-15·70], eating roadside food (aOR 2·91, 95% CI 1·24-6·81), not disposing of children's faeces in a latrine (aOR 15·76, 95% CI 1·54-161·25), not treating drinking water with chlorine (aOR 3·86, 95% CI 1·63-9·14), female gender (aOR 2·43, 95% CI 1·09-5·43), and childhood age (10-17 years) (aOR 7·14, 95% CI 1·97-25·83). This is the first epidemiological study of cholera reported from a setting of semi-nomadic pastoralism in sub-Saharan Africa. Public health interventions among semi-nomadic pastoralists should include a two-faceted approach to cholera prevention: intensive health education programmes to address behaviours inherited from insecure nomadic lifestyles, as well as improvements in water and sanitation infrastructure. The utilization of community-based village health teams provides an important method of implementing such activities.     

Risk factors for measles infection in 0–7 month old children in China after the 2010 nationwide measles campaign: A multi-site case–control study, 2012–2013

IntroductionEndemic measles persists in China, despite >95% reported coverage of two measles-containing vaccine doses and nationwide campaign that vaccinated more than 100 million children in 2010. We performed a case–control study in six Chinese provinces during January 2012 through June 2013 to identify risk factors for measles infection among children aged 0–7 months.MethodsChildren with laboratory-confirmed measles were neighborhood matched with three controls. We interviewed parents of case and control infants on potential risk factors for measles. Adjusted matched odds ratios (mOR) and 95% confidence intervals (CIs) were calculated by multivariable conditional logistic modeling. We calculated attributable fractions for risk factors that could be interpreted as causal.ResultsEight hundred thirty cases and 2303 controls were enrolled. In multivariable analysis, male sex (mOR 1.6 [1.3, 2.0]), age 5–7 months (mOR 3.9 [3.0, 5.1]), migration between counties (mOR 2.3 [1.6, 3.4]), outpatient hospital visits (mOR 9.4 [6.6, 13.3]) and inpatient hospitalization (mOR 107.1 [48.8, 235.1]) were significant risk factors. The calculated attributable fractions for hospital visits was 43.1% (95% CI: 40.1, 47.5%) adjusted for age, sex and migration.ConclusionsHospital visitation was the largest risk factor for measles infection in infants. Improved hospital infection control practices would accelerate measles elimination in China.     

An outbreak of Salmonella Typhimurium DT191a associated with reptile feeder mice

In December 2008 an increase of tetracycline-resistant Salmonella Typhimurium definitive phage-type 191a (DT191a) was identified in England and Wales by the reference laboratory. This was confirmed to have a phage-typing pattern that had not previously been seen. Strong statistical evidence for an association between illness and keeping reptiles was demonstrated by a matched case-case study (mOR 16·82, 95% CI 2·78-∞). Questionnaires revealed an association with frozen reptile feeder mice, and mice representing 80% of the UK supply lines were tested for the presence of Salmonella. DT191a was found in three pools of sampled mice, which were traced back to a single supplier in the USA. Imports from this supplier were halted, and tighter regulations are now in place. A leaflet detailing how to prevent contracting Salmonella from pet reptiles has been published as well as updated advice on the Health Protection Agency's website.     

Contaminated drinking water in one town manifesting as an outbreak of cryptosporidiosis in another

In early 1992 we identified an outbreak of cryptosporidiosis in Oregon and sought to identify and control its source. We used a series of studies to identify risk factors for illness: (i) a case-control study among employees of a long-term-care facility (LTCF); (ii) a matched case-control study of the general community; (iii) a cohort study of wedding attendees; and (iv) a cross-sectional survey of the general community. Drinking Talent water was associated with illness in the LTCF (OR = 22.7, 95 % CI = 2.7-1009.0), and in the community (matched OR = 9.5, 95% CI 2.3-84.1). Drinking Talent water was associated with illness only among non-Talent residents who attended the wedding (P < 0.001) and in the community (RR = 6.5, 95 % CI 3.3-12.9). The outbreak was caused by contaminated municipal water from Talent in the absence of a discernible outbreak among Talent residents, suggesting persons exposed to contaminated water may develop immunity to cryptosporidiosis.     

Risk factors for Nipah virus encephalitis in Bangladesh

Nipah virus (NiV) is a paramyxovirus that causes severe encephalitis in humans. During January 2004, twelve patients with NiV encephalitis (NiVE) were identified in west-central Bangladesh. A case-control study was conducted to identify factors associated with NiV infection. NiVE patients from the outbreak were enrolled in a matched case-control study. Exact odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by using a matched analysis. Climbing trees (83% of cases vs. 51% of controls, OR 8.2, 95% CI 1.25-infinity) and contact with another NiVE patient (67% of cases vs. 9% of controls, OR 21.4, 95% CI 2.78-966.1) were associated with infection. We did not identify an increased risk for NiV infection among persons who had contact with a potential intermediate host. Although we cannot rule out person-to-person transmission, case-patients were likely infected from contact with fruit bats or their secretions.     

A tradition and an epidemic: determinants of the campylobacteriosis winter peak in Switzerland

Campylobacteriosis is the most frequently reported food borne infection in Switzerland. We investigated determinants of infections and illness experience in wintertime. A case–control study was conducted in Switzerland between December 2012 and February 2013. Cases were recruited among laboratory-confirmed campylobacteriosis patients. Population-based controls were matched according to age group, sex and canton of residence. We determined risk factors associated with campylobacteriosis, and help seeking behaviour and illness perception. The multivariable analysis identified two factors associated with an increased risk for campylobacteriosis: consumption of meat fondue (matched odds ratio [mOR] 4.0, 95 % confidence interval [CI] 2.3–7.1) and travelling abroad (mOR 2.7, 95 % CI 1.1–6.4). Univariable analysis among meat fondue consumers revealed chicken as the type of meat with the highest risk of disease (mOR 3.8, 95 % CI 1.1–13.5). Most frequently reported signs and symptoms among patients were diarrhoea (98 %), abdominal pain (81 %), fever (66 %), nausea (44 %) and vomiting (34 %). The median perceived disease severity was 8 on a 1-to-10 rating scale. Patients reported a median duration of illness of 7 days and 14 % were hospitalised. Meat fondues, mostly “Fondue chinoise”, traditionally consumed during the festive season in Switzerland, are the major driver of the epidemic campylobacteriosis peak in wintertime. At these meals, individual handling and consumption of chicken meat may play an important role in disease transmission. Laboratory-confirmed patients are severely ill and hospitalisation rate is considerable. Public health measures such as decontamination of chicken meat and improved food handling behaviour at the individual level are urgently needed.     

Modifiable risk factors for invasive meningococcal disease during an Edmonton, Alberta outbreak, 1999-2002

BACKGROUND: An outbreak of invasive meningococcal disease (IMD) in metro Edmonton, Alberta, Canada between December 1999 and June 2002 resulted in 84 laboratory-confirmed cases. Most cases were infected with Neisseria meningitidis serogroup C, and the highest age-specific incidence was observed in the 15-19 year age group. METHODS: A case-control study was conducted to identify modifiable IMD risk factors among outbreak cases. Two controls were matched to each case on age and sex, and were recruited through random-digit dialing. A questionnaire was telephone-administered to 132 study participants (44 cases, 88 controls). Conditional logistic regression was utilized to calculate risk measures. RESULTS: Multivariate analysis revealed three statistically significant risk factors: bar patronage (OR 35.2; 95% CI: 2.64-468), "rave" attendance (OR 12.8; 95% CI: 1.47-111) and maternal smoking (OR 8.88; 95% CI: 1.67-47.4). Humidifier use in the home was protective (OR 0.07; 95% CI: 0.009-0.64). CONCLUSION: While the precision of risk estimates was low in the multivariate model, this study has identified rave attendance as an emergent IMD risk factor.     

Sexual Contact as Risk Factor for Campylobacter Infection,Denmark

Campylobacteriosis is a disease of worldwide importance, but aspects of its transmission dynamics, particularly risk factors, are still poorly understood. We used data from a matched case-control study of 4,269 men who have sex with men (MSM) and 26,215 controls, combined with national surveillance data on Campylobacter spp., Salmonella spp., and Shigella spp., to calculate matched odds ratios (mORs) for infection among MSM and controls. MSM had higher odds of Campylobacter (mOR 14, 95% CI 10–21) and Shigella (mOR 74, 95% CI 27–203) infections, but not Salmonella (mOR 0.2, 95% CI 0–13), and were less likely than controls to have acquired Campylobacter infection abroad (χ² = 21; p<0.001). Our results confirm that sexual contact is a risk factor for campylobacteriosis and also suggest explanations for unique features of Campylobacter epidemiology. These findings provide a baseline for updating infection risk guidelines to the general population.     

Waterborne cholera outbreak following Cyclone Aila in Sundarban area of West Bengal, India, 2009

Following Cyclone Aila, a block of Sundarban area, West Bengal, India, reported an increased number of diarrhoea cases at the end of May 2009. This study was performed to identify the agent and source of the outbreak as well as to propose control measures. The outbreak is described by time, place and person. A matched case-control study was conducted and rectal swabs and water specimens were collected. In total, 1076 probable case patients and 14 deaths (attack rate 44/10 000) were identified. Vibrio cholerae El Tor Ogawa was isolated from two of five probable case patients’ stool specimens. The outbreak started in the fourth week of May, with two peaks in the second and fourth weeks of June, and lasted until August 2009. Compared with controls, cases were more likely to drink non-chlorinated piped water [matched odds ratio (MOR) = 16, 95% CI 4.9-51; population attributable fraction 58%) and were less likely to drink chlorine-treated water (MOR = 0.06, 95% CI 0.02-0.18). Villagers broke the water pipelines near their houses for easy access to water. Piped water specimens and stored drinking water were positive for faecal contamination. Contaminated drinking water was the probable source of the cholera outbreak. Repairing the pipelines, chlorination at household level and educating villagers regarding the danger of breached water pipe connections controlled the outbreak.