Noroviruses trigger acute inflammation of the gastrointestinal tract and occur worldwide, mainly during the winter months from November to April. Hygiene measures – especially hand disinfection – must be carried out consistently to prevent and control their spread. Noroviruses are nonenveloped viruses that require particularly powerful disinfectants.
Infection, symptoms and course of the disease
Noroviruses are excreted via stool and vomit. They are transmitted by the faecal-oral route via direct (hands) or indirect contact (hand contact with contaminated surfaces). Furthermore, transmission may occur via droplets that are released during explosive vomiting, or via contaminated food.
Infected patients can release up to 10 million norovirus particles per gram of stool. The high virus concentration favours the spread of the pathogen, especially when considering that only 10 to 100 virus particles are enough to trigger an infection. Hence, clinics and other medical inpatient facilities should immediately isolate norovirus-infected patients. Cohort isolation of several infected patients may also be considered.
Symptoms of acute norovirus gastroenteritis include vomiting and severe diarrhoea, often accompanied by sickness, fatigue, pain in the stomach, headache and elevated body temperature. Once infected, it takes 6 to 50 hours until the onset of the disease. Risk of infection is highest during acute symptoms that usually last for 12 to 48 hours. However, the virus may be excreted up to two weeks after the clinical symptoms have subsided – sometimes even much longer.
Hand disinfection in case of noroviruses
For inactivating noroviruses, hygienic hand disinfection is of particular importance and should be performed in accordance with WHO’s Five Moments. In case of norovirus, hand disinfection is obligatory in the following situations:
- after touching a patient
- after glove removal
- before leaving the room
Precondition for adhering to hand disinfection protocols is a sufficient number of dispensers in proper locations.
Hand disinfectants need to be adapted to the existing risk of infection. In case of norovirus outbreaks, WHO recommends using alcohol-based hand disinfectants1. Also the European Committee for Standardization (CEN) emphasises the importance of hand disinfection in case of noroviruses. Since October 2013, the murine norovirus (MNV) has been included as test virus (efficacy testing of hand disinfectants) in the EN 144762.
Surface disinfection in case of noroviruses
The disinfection of surfaces plays an important role in inactivating noroviruses, as the pathogen may persist on inanimate surfaces, e.g. light switches, bedside tables or work surfaces, for up to seven days and remain infectious there.
For norovirus outbreaks, the CDC3 recommendations include:
- Isolation and cohorted areas: routine cleaning and disinfection of frequently touched surfaces and objects – e.g. toilets, bedframes, door handles – with EPA-approved products (label claim: for use in health care). Manufacturer’s instructions on use and exposure time need to be followed
- Wards/patient care areas: frequently touched near-patient surfaces are to be cleaned and disinfected three times a day
- Procedure: cleaning and disinfection of surfaces starting from the areas with a lower likelihood of norovirus contamination (tray tables, counter tops) to areas with highly contaminated surfaces (toilets, bathroom fixtures). Mop heads need to be changed when new solutions are prepared and after cleaning organic materials (stool, vomiting).
Background: Surrogate virus MNV
Human norovirus does not replicate in cell cultures. Hence, efficacy testing of disinfectants usually is carried out with murine norovirus (MNV). MNV is suited as test virus due to its morphological similarities to the human norovirus.