What is Norovirus?

Norovirus, also known as Norwalk Viruses (NV ^[1] ), is a virus of the genus Norovirus (NV) in the Human Calicivirus (HuCV) family. It is a group of virus particles with similar morphology and slightly different antigenicity.

In 1968, scientists isolated a viral pathogen in the stools of patients with an acute diarrhea that broke out in Novak, USA. Since then, various virus-like particles with similar morphology but slightly different antigenicity have been isolated from the stools of patients with gastroenteritis around the world, all named after the place of discovery, such as Hawaii Virus (HV), Snow Mountain Virus (SMV) , Mexico Virus (MxV), Southampton Virus (SOV), etc., first known as Small Round Structural Virus (SRSV), and later known as Norwalk-like virus (NLV). In 1995, China reported the first case of norovirus infection. Since then, there have been multiple outbreaks of norovirus-infected diarrhea across the country. In August 2002, the eighth international virus naming committee approved the name of the virus as Norovirus (NV). ^[1]

Norovirus mutates quickly, has strong environmental resistance, low infection dose, short incubation period after infection, long detoxification time, short immune protection time, and multiple transmission routes. The ability to spread quickly. The main manifestation of norovirus infection is diarrhea and / or vomiting, which is commonly referred to as acute gastroenteritis internationally. In China, it has been included in category C infectious diseases as "other infectious diarrhea diseases (except cholera, bacterial and amoebic dysentery, typhoid fever and paratyphoid fever)" for reporting management. This has affected reports of norovirus infections and their outbreaks with vomiting as the main symptom. Norovirus is the main cause of sporadic cases and outbreaks of global acute gastroenteritis, with a serious disease burden ^[3]

In 1968, an outbreak of acute gastroenteritis occurred in a primary school in Norwalk, USA. In 1972, Kapikian and other scientists found a virus particle with a diameter of about 27 nm in the feces of patients who had the outbreak. They named it Norwalk virus. ^[5]

(I) Incubation period

Noroviruses have a relatively short incubation period, usually 12-48 hours. Sweden has analyzed data from an outbreak involving 30 child care institutions and school-age child care institutions caused by foodborne transmission, with a median incubation period of 34 hours (range: 2-61 hours). A systematic review summarized the incubation period of Norovirus in the GI and GII gene groups, with median values of 1.1 days (95% CI: 1.1-1.2 days) and 1.2 days (95% CI: 1.1-1.2 days). Different genes There is no significant difference in the incubation period of the group ^[13]

(1) Burden of disease

There are three main methods for estimating the norovirus disease burden: Through establishing a national surveillance system or representative sentinel surveillance system based on population and pathogen-based surveillance, directly calculate the number of cases, hospitalizations, and severe cases caused by norovirus each year. And the number of deaths; Based on the overall disease burden of acute gastroenteritis and the etiology of acute gastroenteritis of different severity, extrapolate the disease burden of norovirus infection to acute gastroenteritis; Use regression models to estimate. At present, there are still major difficulties in directly and accurately assessing the burden of Norovirus disease. The main reasons are: most countries around the world do not have a national surveillance system based on Norovirus cases; there are no sensitive and rapid tests for clinical use Methods; Most patients with acute gastroenteritis did not seek medical treatment, and only a small number of patients in the medical cases collected specimens for pathogen detection. ^[4]

(A) suspected cases

That is, acute gastroenteritis cases are defined as those who have defecation 3 times within 24 hours and have changed traits (shown as watery stools), and / or vomiting 2 times within 24 hours. ^[4]

(I) Aggregated epidemic situation:

Within 3 days, 5 or more epidemic-associated norovirus infections occurred in the same school, childcare institution, medical institution, nursing home, factory, construction site, cruise ship, community / village and other collective units or places. Two cases were laboratory diagnosed cases. ^[4]

(1) When a collective outbreak or outbreak of acute gastroenteritis is found in a collective unit or place such as a school, child care institution, medical institution, nursing home, factory, construction site, cruise ship, etc., it shall immediately call the county / district level by telephone or fax. CDC report.

(2) The territorial disease prevention and control center shall promptly conduct an investigation after receiving the epidemic report, and verify the epidemic situation based on the epidemiology of the epidemic, clinical manifestations of the case, and laboratory test results.

(3) For any outbreak of norovirus infection diagnosed in the laboratory, the number of cases should be counted strictly according to the definition of the case, including those mainly with vomiting symptoms. Norovirus infections that meet the reporting standards of the "National Public Health Emergency-Related Information Reporting Management Practices (Trial)", the Terrestrial Disease Prevention and Control Center should report relevant information through the public health emergency management information system ^[4]

The investigation process and content of the clustered epidemic and outbreak are the same, mainly including the basic situation investigation of the outbreak occurrence institution, on-site epidemiological investigation, hygienic investigation and termination evaluation of the epidemic. For the specimen collection and laboratory testing involved in the investigation, see "eight , Laboratory testing. " ^[4]

(I) Specimen Collection

A variety of pathogens can cause aggregation or outbreaks of acute gastroenteritis. Full consideration should be given to the special requirements for specimen collection and storage of different pathogen detections. Therefore, for the same collection object, multiple specimens should be collected, packed and stored in accordance with different requirements of bacteria, viruses, parasites, etc., in order to do other pathogen detection, review experimental results or further identification if necessary. A sample information registration form is required when sampling.

1. specimen type

Poop

Fecal specimens are preferred for Norovirus testing. 5g or 5ml or more of each specimen is placed directly in a clean, sterile, dry, closed container. Do not add any protective agent, culture medium, detergent or metal ions in the container, and do not dilute.

Zygomatic anal swab

Anal swab specimens cannot be stored for a long time, and the detection rate is lower than that of fecal specimens. When anal swab contains a small amount of stool, if the test result is weakly positive, the result is easily misjudged, leading to false negatives. When collecting, note that there should be visible feces on the anal swab, and put it in a closed sealed tube with a sterile cover. The sampling tube should contain 2ml of sterile PBS buffer or Hank's solution. The liquid should not pass the swab part of the anal swab, and it should be tested as soon as possible. ^[4]

Currently, there are no specific antiviral drugs and vaccines against Norovirus. The main prevention and control measures are non-drug preventive measures, including case management, hand hygiene, environmental disinfection, food and water safety management, risk assessment and health education. These measures apply both to the management of clusters and outbreaks, and to the prevention and control of sporadic cases. ^[4]

On November 23, 2018, a cluster of vomiting occurred in Dalian Hongmei Primary School in Liaoning. As of 17:00 on that day, a total of 176 people (including 175 students and 1 teacher) at the school had vomited. The preliminary determination was that norovirus was caused, and all of them had been reported to the local CDC for treatment. ^[16]

On February 10, 2019, many tourists from Yabuli First Resort in Heilongjiang had suspected food poisoning symptoms such as diarrhea, abdominal pain, vomiting, and fever after dining at the resort. Tested by the Harbin Center for Disease Control and Prevention, it was determined that some tourists in the resort had symptoms of vomiting and diarrhea as norovirus infection. With timely treatment by medical staff, the patient's condition was effectively controlled. ^[17] After overnight testing by the Harbin Center for Disease Control and Prevention, it was determined that some tourists at Club Med ( Yabuli Mediterranean Club ) experienced vomiting and diarrhea as norovirus infection. According to the introduction of the Harbin Health and Health Committee, after receiving the report, the Harbin Health and Health Committee immediately launched an emergency plan, and the Harbin Disease Prevention and Control Center quickly assembled personnel from relevant departments such as emergency, food safety, infectious disease, and inspection to form an investigation team. Rush to the scene to investigate and dispose of it for a while. After investigation, a total of 42 self-reported symptomatic tourists were registered, 8 of whom went to the Yabuli Town Central Health Center and the Yabuli Lin District People's Hospital for treatment. Two were diagnosed with acute gastroenteritis, and there were no hospitalized patients. At present, according to the clinical manifestations of patients and the results of overnight testing in the laboratory of the Harbin Center for Disease Control and Prevention, the patients are identified as norovirus infection. With timely treatment by medical staff, the patient's condition was effectively controlled. ^[18]

From the evening of March 15th to 12 noon on March 17, 2019, 31 students in Fujian Polytechnic School developed vomiting and diarrhea. After treatment by the Fuzhou Air Force Hospital and the Jinshan Branch of the Provincial Hospital, the condition has been controlled and there are no hospitalized cases. The samples collected from some diseased students in the Cangshan District Center for Disease Control and Prevention in Fuzhou City are preliminarily judged to be Norovirus infection. The specific situation must be further determined by the Fuzhou Center for Disease Control and Prevention. ^[19]

On July 15, 2019, the Beijing Chaoyang District Government informed that residents of some communities in Chaoyang Dougezhuang had diarrhea, and the disease control department immediately launched an investigation. As of 20:00 on July 14th, 49 people had come to the hospital for treatment, 105 people had reported no symptoms, and 52 samples had detected norovirus. Relevant departments have taken water samples for testing and investigated all water supply networks. ^[20]

On November 25, 2019, a Norovirus outbreak broke out on a cruise ship in the United States called the "Norway True Joy". The cruise ship departed from Florida and arrived at the Port of Los Angeles after 16 days of sailing. Hundreds of passengers on board were evacuated by the Los Angeles Fire Department medical staff after the cruise ship entered the port. Passengers seeking medical assistance have been examined and treated. Among them, some sick passengers have been quarantined after disembarking. ^{[twenty one]}