Outbreaks of Norwalk-like viral gastroenteritis--Alaska and Wisconsin, 1999

Norwalk-like viruses (NLVs) are the most common cause of epidemic gastroenteritis in the United States, resulting in illness in approximately 23 million persons each year . Persons of all ages are affected because previous infection confers only short-term immunity. Most NLV gastroenteritis outbreaks involve foodborne or person-to-person transmission. This report presents investigations of a foodborne NLV outbreak in Alaska and person-to-person transmission in Wisconsin.     

A school outbreak of Norwalk-like virus: evidence for airborne transmission

An outbreak of gastroenteritis affected a school attended by children aged 4-11 years. Epidemiological features suggested this was due to Norwalk-like virus (NLV) and this was confirmed by polymerase chain reaction (PCR). Nucleotide sequence analysis of the PCR amplicons revealed identical strains in all five positive stool samples. Pupils were significantly more likely to become ill following an episode of vomiting within their classroom (adjusted odds ratio 4.1, 95% CI 1.8-9.3). The times from exposure to illness were consistent with direct infection from aerosolized viral particles where exposure to vomiting was high. Cleaning with quaternary ammonium preparations made no impact on the course of the outbreak. However, the outbreak stopped after the school closed for 4 days and was cleaned using chlorine-based agents. This study confirms the importance of vomiting in the transmission of NLV and provides evidence that direct infection with aerosolized viral particles occurs.     

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.     

Waterborne outbreak of Norwalk-like virus gastroenteritis at a tourist resort,Italy

In July 2000, an outbreak of gastroenteritis occurred at a tourist resort in the Gulf of Taranto in southern Italy. Illness in 344 people, 69 of whom were staff members, met the case definition. Norwalk-like virus (NLV) was found in 22 of 28 stool specimens tested. The source of illness was likely contaminated drinking water, as environmental inspection identified a breakdown in the resort water system and tap water samples were contaminated with fecal bacteria. Attack rates were increased (51.4%) in staff members involved in water sports. Relative risks were significant only for exposure to beach showers and consuming drinks with ice. Although Italy has no surveillance system for nonbacterial gastroenteritis, no outbreak caused by NLV has been described previously in the country.     

肇庆市某幼儿园诺瓦克样病毒性胃肠炎爆发情况调查

目的:对肇庆市某幼儿园一起诺瓦克样病毒引起的群体性胃肠炎进行调查和分析。方法:采取面对面或电话问卷调查的方法收集病例发病时间、班级分布、性别年龄分布等资料,进行流行病学分析。结果:89例病例中幼儿园学生56人,教师、保育员9人,学生家长24人,罹患率分别为9.3%、12.7%、8.3%;学生发病主要集中在6个班级,年龄集中在6岁以下,平均病程3.7天。实验室检测10份粪便ELISA诺瓦克病毒抗原阳性5份,PCR检测阳性8份。结论:本起群体性胃肠炎是由诺瓦克样病毒引起,今后要加强幼托机构对新发传染病的防治工作。     

Widespread environmental contamination with Norwalk-like viruses (NLV) detected in a prolonged hotel outbreak of gastroenteritis

A protracted outbreak of Norwalk-like virus (NLV)-associated gastroenteritis occurred in a large hotel in North-West England between January and May 1996. We investigated the pattern of environmental contamination with NLV in the hotel during and after the outbreak. In the ninth week, 144 environmental swabs taken from around the hotel were tested for NLV by nested RT-PCR. The sites were categorized according to the likelihood of direct contamination with vomit/faeces. The highest proportion of positive samples were detected in directly contaminated carpets, but amplicons were detected in sites above 1.5 m which are unlikely to have been contaminated directly. The trend in positivity of different sites paralleled the diminishing likelihood of direct contamination. A second environmental investigation of the same sites 5 months after the outbreak had finished were all negative by RT-PCR. This study demonstrates for the first time the extent of environmental contamination that may occur during a large NLV outbreak.     

A norwalk-like virus waterborne community outbreak in a Swedish village during peak holiday season

An outbreak of gastroenteritis due to Norwalk-like virus (NLV) affecting approximately 500 people occurred in a Swedish ski resort during February-March 2002. Epidemiological investigations were performed on cohorts of schoolchildren, permanent residents and skiers visiting the area. Attack rates were respectively 39.7, 29.9 and 38.5%. Drinking un-boiled water originating from one of the three communal water systems was a significant risk factor for all groups. For schoolchildren, the risk of illness increased with increasing amount of water consumed. Nine of 12 stool samples of patients analysed tested positive for NLV. The water tested negative for indicator bacteria and results of NLV tests were inconclusive. In the absence of microbiological findings, the environmental authorities were reluctant to act based on the epidemiological analysis alone, and intervention was delayed until mid-April, following the discovery of a crack in a sewage pipe 10 m from the well.     

A norovirus gastroenteritis epidemic in a long-term-care facility.

BACKGROUND: In Victoria, Australia, from July to December 2002, 126 outbreaks of viral and suspected viral gastroenteritis were reported in healthcare institutions. Norovirus was found to account for at least 77 of the 126 outbreaks. METHODS: In October 2002, the infection control unit investigated an outbreak of acute gastroenteritis on three wards in a 500-bed, long-term-care facility in Melbourne, Victoria, Australia. Cohorting and other infection control measures were initiated. RESULTS: The outbreak was controlled 32 days after the first symptoms of acute gastroenteritis were identified. Fifty-two patients and 11 staff members were affected. Norovirus genotype 2 was detected on two of the three wards. Norovirus was not isolated in the third ward but was suspected to be the causative organism. CONCLUSIONS: Outbreaks of viral gastroenteritis can cause significant morbidity in a long-term-care facility, affecting both patients and staff. In addition, the transmission of viral pathogens can be well established before there is recognition of an outbreak.     

Norwalk-like viral gastroenteritis in U.S. Army trainees--Texas, 1998

During August 27-September 1, 1998, 99 (12%) of 835 soldiers in one unit at a U.S. Army training center in El Paso, Texas, were hospitalized for acute gastroenteritis (AGE). Their symptoms included acute onset of vomiting, abdominal pain, diarrhea, and fever. Review of medical center admission records for AGE during the previous year indicated that fewer than five cases occurred each month. This report describes the outbreak investigation initiated on August 30 by a U.S. Army Epidemiologic Consultation Service (EPICON) team; the findings indicated the outbreak was caused by a Norwalk-like virus (NLV).     

Practical lessons from the management of an outbreak of small round structured virus (Norwalk-like virus) gastroenteritis

An outbreak of viral gastroenteritis caused illness in 92 people during October 2000. All the cases had an association with one hotel and 80% of cases identified had attended one of two buffet meals on 18th October 2000. Cohort analysis did not implicate any particular foodstuff in this outbreak. All bacteriological tests on food samples were negative. Small round structured virus (SRSV)/Norwalk-like virus (NLV) particles were seen by electron microscopy in 6 out of 27 stool samples submitted for analysis. This paper describes the outbreak and in particular the lessons learned from the management and control of it. These include practical points with regard to the outbreak control team, liaison with the microbiology laboratory, handling data, agreeing a case definition, and occupational health issues. All can be applied elsewhere by those responsible for managing outbreaks at a local level.     

一起医院内集聚性诺如病毒胃肠炎的调查

目的 调查分析一起在上海市徐汇区某社区卫生服务中心内科病房内发生的集聚性诺如病毒GⅡ型胃肠炎疫情的特征及其原因.方法 采用统一的集体性腹泻个案调查表进行现场流行病学调查,使用病例对照研究方法分析相关危险因素,采用RT-PCR方法检测病毒核酸.结果 该起疫情共报告病例22例,发病率为31.0％,以呕吐腹泻为主要临床表现,疫情流行持续8d,引入率为30.3％;时间分布呈单峰,空间分布有集聚性;通过实验室检测确定有两名护工隐性感染,在11份粪便、肛拭标本中检出9份诺如病毒GⅡ型核酸阳性,6份环节标本呈核酸阴性;由隐性感染护工护理的患者发病率高于非感染护工护理的患者(x2 =4.98,P=0.026),OR值为11.2(95％ CI=1.80～116.80);空间分布的集聚性与隐性感染护工护理的床位高发病率有较好的一致性.结论 该次疫情是一起发生在医疗机构内由诺如病毒GⅡ型引起的集聚性胃肠炎疫情,隐性感染的护工是传染源之一,接触传播是重要的传播途径;该次疫情在对手卫生、标准防护执行力进行干预及落实各项消毒隔离措施后得到有效控制.     

Sensor, a population-based cohort study on gastroenteritis in the Netherlands: incidence and etiology

A prospective population-based cohort study with a nested case-control study was conducted to estimate the incidence of gastroenteritis and the associated pathogens in the general Dutch population. Follow-up of two consecutive cohorts was performed by weekly reporting cards from December 1998 to December 1999. Cases and controls in the case-control study supplied a questionnaire and stool samples. The standardized gastroenteritis incidence was 283 per 1,000 person-years. The incidence rose with increasing level of education and was higher for persons with a history of diarrhea and for young children. Bacterial pathogens accounted for 5% of cases, bacterial toxins for 9%, parasites for 6%, and viral pathogens for 21%, with Norwalk-like virus (NLV) as the leading pathogen in 11% of cases. The gastroenteritis incidence was higher than that reported for England, but lower than for the United States. In community cases, viral pathogens are the leading cause of gastroenteritis, with NLV being the number one cause of illness in all age groups but one. In many countries, preventive measures are implemented to decrease bacterial infections. However, additional prevention of viral infections, especially NLV, might significantly decrease the number of gastroenteritis cases in the community.     

Outbreak of Norwalk virus in a Caribbean island resort: application of molecular diagnostics to ascertain the vehicle of infection

In 1998, an outbreak of gastroenteritis affected at least 448 persons including 122 staff at a resort hotel in Bermuda. A survey among staff indicated that gastroenteritis was associated with eating or drinking at the hotel (OR = 60, 95% CI = 2.4-15.1). Multiple specimens of drinking water had elevated faecal coliform levels and Escherichia coli present, suggestive of faecal contamination. Stools from 18 of the 19 persons with gastroenteritis that were tested were positive for genogroup-II Norwalk-like viruses (NLVs). RT-PCR analysis of a 31 specimen of water produced a genogroup-II NLV genome with a sequence identical to that of NLVs in the stools of three ill persons. This outbreak shows the value of new molecular diagnostics to link illness with a contaminated source through the use of sequence analysis. The risk of outbreaks such as these could be reduced in tourism dependent regions like Bermuda and the Caribbean by regular evaluation of data from the inspection and monitoring of drinking water supplies and waste water systems, by ensuring the chlorination of supplemental drinking water supplies and by establishing food-safety initiatives.     

一起医院住院病人诺如病毒急性胃肠炎暴发疫情的 调查

摘要:目的　调查某医院住院病人腹泻暴发疫情的致病因子,找出传染源和危险因素,提出针对性的预防控制建议,有效控制疫情。方法　采用统一的调查表对病例进行流行病学调查;开展现场卫生学调查并采集便标本,采用RT-PCR对便标本进行诺如病毒核酸检测。结果　调查该病区暴露的住院患者和医务人员135名,发现22名病例,罹患率为16.30%;患者临床表现以腹泻、恶心、呕吐为主,部分患者出现发热症状;不同楼层住院老人罹患率差异无统计学意义（χ2＝0.82,P＞0.05）;住院老人罹患率高于护工（χ2＝5.35,P＜0.05）,不同性别住院老人发病风险相同（χ2＝0.18,P＞0.05）;采集的14份便标本中,8份检测结果为诺如病毒核酸阳性。结论　该次急性胃肠炎暴发疫情是由诺如病毒引起,传染源可能为隐形感染者或病原携带者,病毒通过某种共用媒介传播后再以人-人传播模式进一步扩散,高危人群为住院老人;采取针对性措施后,疫情得以有效控制。     

Transmission of a small round structured virus by vomiting during a hospital outbreak of gastroenteritis

An outbreak of gastroenteritis due to a small round structured virus (SRSV) (Norwalk-like virus) occurred in an elderly care unit, affecting a total of 126 patients and staff. The outbreak caused major disruption to the provision of health care services by the unit over a 3-week period. Following the outbreak a study was undertaken to explore risk factors for acquisition of SRSV infection by health care workers on the unit. Exposure to patients nearby who were vomiting and the number of close contacts with ill patients were significantly related to the risk of developing gastroenteritis (P < 0·05). No significant increase in risk of developing gastroenteritis was found in nurses who cleaned vomit or faeces from affected patients. The findings suggest that aerosolization of vomit was of major importance in transmission of infection during the outbreak; the implications for infection control are discussed.