Just because food is fresh and hygienic, it cannot prevent diseases from entering the body through eating

Author: Chen Dianjie, Fifth Medical Center, PLA General Hospital

Reviewer: Zhang Jieli, Deputy Chief Nurse, Fifth Medical Center, PLA General Hospital

"I told you not to eat ice cream but you insisted on eating it. Look, you have diarrhea now!"

When you see the above sentence, do you seem to hear a voice in your ears?

I believe you are familiar with this statement. When symptoms of vomiting and diarrhea occur, many people may first check the diet for the culprit.

Diarrhea is not necessarily caused by food poisoning or catching a cold, it may also be an infectious disease. In the hot summer, frequent intake of cold drinks and cold food, the temperature that is conducive to the survival of some pathogens, and the more fragile gastrointestinal environment all make digestive tract infectious diseases more likely to occur.

The pathogens that cause infectious diseases are not necessarily transmitted through food. Ice cream, watermelon, flavored shrimp... may really be blamed.

Figure 1 (copyright image from the gallery, unauthorized reproduction)

Taking the norovirus, which is easy to infect in autumn and winter, as an example, the virus can be transmitted from person to person, through food, and through water. Human-to-human transmission can be through the fecal-oral route (including ingestion of aerosols produced by feces or vomitus) or indirect contact with an environment contaminated by excrement. Foodborne transmission is through eating food contaminated by norovirus. The contamination link can occur when catering workers infected with norovirus contaminate food during meal preparation and service, or when food is contaminated by human excrement containing norovirus during production, transportation, and distribution. Waterborne transmission can be caused by the contamination of drinking water sources such as bottled water, municipal water supply, and well water [1].

Research data shows that food-borne and water-borne transmission are not the most mainstream routes of norovirus transmission.

Figure 2 The route of Norovirus infection (Source: Fields Virology, 6th, Ed, P597)

The ability to transmit from person to person is also an important reason why the Norovirus spreads quickly in closed places (such as childcare institutions, kindergartens, schools, nursing homes, cruise ships, etc.) and is prone to cause outbreaks.

Scientists discovered that the Norovirus originated from an outbreak of acute gastroenteritis in an elementary school in Norwalk, USA in 1968.

In 1972, scientists discovered a virus particle with a diameter of about 27nm in the feces of patients in the outbreak and named it Norwalk virus, later also known as Norovirus, Norwalk virus or Pyovirus.

In 2002, the Eighth International Committee on Nomenclature of Viruses renamed Norwalk virus, Norovirus, Norwalk virus, and Pyogenic virus as Norovirus, which became an independent genus of the Caliciviridae family - Norovirus.

Figure 3 from the website of the International Committee on Taxonomy of Viruses

Norovirus can cause acute gastroenteritis, which manifests as diarrhea, vomiting, nausea, or accompanied by fever, headache and other symptoms. Children are more likely to suffer from vomiting and nausea, while adults are more likely to suffer from diarrhea. Because the incidence rate is higher in winter, it is also called winter vomiting disease.

Norovirus outbreaks in my country are reported through the National Public Health Emergency Surveillance System. Of the 692 acute gastroenteritis outbreaks reported from January 2014 to December 2017, norovirus was the dominant pathogen, accounting for approximately 89% (616/692). Of the 616 norovirus outbreaks, involving approximately 30,000 cases, 93% (571/616) of the outbreaks occurred in schools, and 63% (387/616) of the outbreaks were transmitted through human-to-human contact [2].

Norovirus-induced diarrhea is a self-limiting disease with symptoms lasting an average of 2 to 3 days and no sequelae after recovery. However, some patients may experience dehydration due to continuous diarrhea, which can be life-threatening in severe cases.

There is currently no specific antiviral drug, and symptomatic or supportive treatment is the main treatment. Dehydration is the main threat of Norovirus-induced diarrhea. Severe patients, especially young children and the weak, should be given timely infusion or oral rehydration to correct dehydration, acidosis and electrolyte imbalance.

Norovirus is mainly excreted through the patient's feces and can also be excreted through vomitus. Norovirus is not only cold-resistant, but also heat-resistant, and can survive in a temperature range of 0 to 60°C. General disinfectants such as 20% ether and 3.75 to 6.25 mg/L of chloride ions in ordinary drinking water are ineffective against it. Ethanol and hand sanitizer cannot inactivate it.

Figure 4 (copyright image from the gallery, unauthorized reproduction)

Norovirus can be inactivated by boiling at 100°C or using a high concentration of chloride ions of 10 mg/L (the chloride ion concentration used in sewage treatment).

There is currently no vaccine to prevent norovirus, and its prevention and control mainly adopts non-drug preventive measures:

Develop good hygiene habits : follow the "two do's and two don'ts". Wash your hands after returning home, before meals, and after going to the toilet. Keep raw and cooked food separate. Don't drink raw water, and don't eat raw seafood, aquatic products, or uncooked food.

Disinfection : (1) Boiling disinfection: Regularly boil the tableware for disinfection, and make sure the tableware is completely covered with water for 15 to 20 minutes; (2) Sun exposure disinfection: After washing, towels, bedding, etc. should be exposed to the sun for at least 6 hours.

Others : Pay attention to opening windows frequently for ventilation, etc.

When caring for patients infected with norovirus, it is also necessary to pay attention to disinfection and isolation. Specific precautions are as follows:

Since patients will produce viral aerosols when vomiting, the room should be ventilated by opening doors and windows regularly. Generally, the room should be ventilated twice a day, each time for 30 minutes.

Wear gloves when caring for patients, especially when cleaning up vomit and excrement, and wear a mask. However, wearing gloves cannot replace hand washing, and you need to wash your hands before and after contact with patients.

When handling items contaminated by patient vomit or excrement, it is necessary to use disposable absorbent materials (such as gauze, rags, etc.) dipped in 5000-10000 mg/L chlorine-containing disinfectant (or high-concentration "84" disinfectant) to completely cover the contaminants, carefully clean them, and avoid contact with contaminants during the cleaning process.

Contaminants in toilet bowls or containers can be carefully poured into (to prevent liquid splashing) a sufficient amount of 5000-10000 mg/L chlorine-containing disinfectant (or high-concentration "84" disinfectant), left to act for more than 30 minutes, and then discharged into the sewage treatment system.

Mops, rags and other tools used in cleaning, and containers containing contaminants must be soaked and disinfected in a disinfectant solution containing 5000 mg/L of effective chlorine (or high-concentration "84" disinfectant) for 30 minutes and then thoroughly rinsed before they can be used again.

Mops for toilets and restrooms should be dedicated.

References

【1】Liao Qiaohong, Ran Lu, Jin Miao, et al. Technical Guidelines for Norovirus Outbreak Investigation and Prevention and Control (2015 Edition). Chinese Journal of Preventive Medicine, 2016, 50(1): 7-16.

【2】Wang Yu, Gao Zhiyong, Jia Lei, et al. Progress in epidemiological research on norovirus infection. Chinese Journal of Epidemiology, 2022, 43(6): 974-980.