Impact of the Covid-19 pandemic restrictions and incidence of norovirus infection

Acute infectious diarrhoea is a common cause of morbidity in the adult population.¹ This can contribute to an increase in mortality in older adults and those with multiple comorbidities.² Norovirus, also referred to as the “winter vomiting-bug”, contributes to a significant proportion of viral gastroenteritis in hospital and care home settings worldwide.^1-5

Genus Norovirus are RNA viruses, belonging to family Caliciviridae. It has 10 genogroups (GI to GX) and 49 genotypes.⁶ Its primary mode of transmission is faecal-oral. There is some evidence that vomitus can leave aerosol particles in the air few for a few hours, some of which can transmit onto surfaces.^5,7 There have been outbreaks in many countries all-year around, with increased prevalence in the colder, winter months.^3,5

The global Covid-19 pandemic has seen the implementation of several non-pharmaceutical interventions (NPIs) to reduce the spread of coronavirus.⁸ We assessed the possible secondary impact of these measures on norovirus incidence and case rates, to see if it indirectly affected transmission at the Royal Berkshire Hospital.

Material and methods

Patient population

From 1st November 2019 to 31st March 2020 and 1st November 2020 to 31st March 2021, patient demographics and the number of admissions onto four elderly-care wards at the Royal Berkshire Hospital (Wards B, E, M and W) were collected via the Trust Intelligence Portal Service.

Data collection and definitions

Using microbiology laboratory data provided by the infection prevention and control team we were able to identify all stool samples processed during these time periods, across all four wards. The patient criteria, mandating a stool sample and testing criteria in the laboratory, remained the same across both data collection periods. All diarrhoeal stool samples received are processed for norovirus G1 and GII, using EntericBio molecular diagnostic system (Serosep).

This data was combined with our Electronic Patient Record (EPR), to determine baseline characteristics.

The sample size was determined by number of admissions during a typical season (November-March), onto a single ward. This was then expanded to include all four wards in the elderly care department, generating a sample of greater than 1,000 admissions across the November to March period.

The mean and range of data sets were calculated. The data sets across both seasons (2019-2020 and 2020-2021) were stratified by individual ward, those requiring a stool sample and those which tested positive for norovirus. Further subgroup stratification amongst those who had tested positive for norovirus, focused on potential confounders.

Results

		2019-20 2020-21
Total number of admissions	1280		1641
No. of patient’s presenting with diarrhoea	197 (15.39%)		113 (6.99%)
No. of stool samples sent (%)	197 (15.39%)		113 (6.99%)
No. of samples norovirus positive (%)	60 (4.68%)		0 (0%)

Between November 2019 and March 2020, there were 1,280 admissions to the four elderly care wards. During this time period, 197 stool samples were sent to microbiology.

The mean age of the patient cohort in 2019-2020 was 86.47 years (range 65-102), with a mean length-of-stay (LOS) of 31.41 days (range 6-84).In the following year from November 2020 to March 2021, there were 1641 admissions across the same ward base. During this time period, 113 stool samples were sent to microbiology.

The mean age of the patient cohort in 2020-2021 was 82.72 years (range 59-99), with a mean length-of-stay (LOS) of 17.9 days (range 1-60).All stool samples sent during 2019-2020 were tested for norovirus, out of which 60 returned positive (30%). In comparison for 2020-2021, 0% of tests returned positive for norovirus.

Of the 60 samples which tested positive in 2019-2020, 20 samples (34%) were positive within 48 hours of admission to hospital, whereas 66% were post 48 hours. There were bay and ward closures on these four wards during this period. However, healthcare workers did not report absence due to diarrhoea and/or vomiting.

Once again the positivity rate in 2020-2021, in our patient cohort and healthcare workers on these four wards was zero.

Discussion

The results indicate a major contrast in norovirus transmission across the two seasons.

Plausible explanations as to the causality for this observed phenomenon must consider the impact of coronavirus restrictions on the environment. The Covid-19 pandemic has had a dramatic effect on human interaction; both outside and inside the hospital setting.

External to healthcare setting

The national “stay-at-home” order enforced during lockdown, in the second wave of the Covid-19 pandemic in the UK, undoubtedly reduced numbers of social interactions. This meant a reduction in chance of human to human contact and therefore possibly also reducing chance of spread of norovirus.

Similarly, the NPIs (hands washing, face masks, and maintaining distance) recommended in the community whilst undergoing essential activities such as using public transport or shopping for groceries, also would have helped somewhat.

Internal to healthcare setting

Enforcement of regular hand washing with soap and water, after each patient contact, would have had a positive impact on reducing norovirus spread on wards between humans and surfaces. This was extended to include portable hand washing facilities with hot water and soap, outside each ward entrance.

The coronavirus pandemic has seen an ongoing evolution of infection, prevention and control (IPC) guidelines.^9,10 Healthcare workers and staff throughout the hospital are required to wear a certain level of personal protective equipment (PPE), depending on the type of clinical encounter. For contact and droplet exposure this includes gloves, apron and a type-IIR surgical mask. For aerosol exposure this is strengthened to full level 3 PPE.^9,10

Whilst the transmission route for coronavirus differs from norovirus, it is possible that there could have been a degree of added protection, in addition to hand-washing. The additional PPE may increase protection from projected particles of vomitus and also cross-contamination from specimen handling; including disposal of waste in a dirty utility. The barrier provided by a face mask could further reduce the chances of a ‘subconscious’ hand to mouth contact.

Similarly an increased focus on patient-spacing during the coronavirus pandemic, also may have helped in reducing nosocomial norovirus transmission.

By the end of 2020, public adherence to non-pharmaceutical interventions for coronavirus was regularly re-enforced, by widespread information campaigns. Similarly, healthcare workers in the community had incorporated this into their daily working practices. This could also explain why we saw a 0% positivity rate during November 2020 to March 2021. This combined with the PPE used in hospital, is likely to have helped further in sustaining the effects of reducing nosocomial spread of norovirus.

Study limitations

The retrospective data in this report looked at four wards in a busy district general hospital. At a local level the focus was within the elderly care department, so it is difficult to comment whether this can be generalised across all wards within the hospital, given case-mix and acuity is likely to vary amongst different medical specialities.

At a regional and national level, it is possible that similar trends were observed as the NPIs were implemented nationwide in the UK, during the Covid-19 pandemic.

The Covid-19 pandemic did indirectly affect health-seeking behaviours, with ONS data showing all-cause mortality to be higher.¹¹ Without being able to quantify the exact community prevalence of norovirus, it is hard to say whether there was an overall reduced incidence in the population. However, a zero percent positivity-rate in 2020-2021, would point towards this.

Furthermore, the reduced total number of stool samples sent in 2020-2021 (approximately 7% of the total admissions compared with 15% in 2019-2020), could therefore point to reduced population transmission and hence a reduction in norovirus case-load seen in the hospital.

One should also bear in mind that whilst norovirus is a common cause of acute gastroenteritis in an inpatient setting, there are other factors contributing to symptoms of diarrhoea and vomiting. These can include malabsorption, inflammatory bowel disease and diverticulitis. In addition medication side effects from antibiotics and laxatives are also prominent.^12,13

It would be pertinent to consider whether the lower number of stool samples being sent was due to a slightly different inpatient population, as a result of the second coronavirus wave.¹⁴ Whilst there was one designated elderly care ward for Covid-19 patient’s (Ward M) throughout November 2020 to March 2021; by January 2021 all of the elderly care wards had started to look after Covid-19 patients. This may have impacted the number of older adults being managed in hospital with other conditions that cause symptoms of diarrhoea and vomiting.

When comparing baseline characteristics our data did show that the average LOS was lower and mortality rate was higher during November 2020 – March 2021. This also may be reflective of acuity and so further analysis over a third consecutive season may be of additional benefit in substantiating potential correlative effects of Covid-19 pandemic NPI’s on norovirus incidence.

Conclusion

This retrospective observational study shows a potential correlation between the NPI’s utilised in controlling the spread of COVID-19 and a reduction in transmission of norovirus,¹⁴ which requires further detailed multi-centre and national analysis.

Although coronavirus is primarily a respiratory virus and norovirus predominantly a gastrointestinal virus; widespread use of PPE during the pandemic, in a way never seen in this country before, could have been a contributing factor.

As such, further studies would be required to elucidate the benefits of implementing such in-hospital measures, beyond the Covid-19 pandemic.

Sumeer Krishan Mittal, Department of Elderly Care, Royal Berkshire Hospital, Reading

Stephanie Bradbury, Department of Elderly Care, Royal Berkshire Hospital, Reading

Ruhel Miah, Department of Elderly Care, Royal Berkshire Hospital, Reading

Matthew Roberts, Department of Elderly Care, Royal Berkshire Hospital, Reading

Patricia Knight, Department of Infection Prevention and Control, Royal Berkshire Hospital, Reading

Nilangi Virgincar, Department of Microbiology, Royal Berkshire Hospital, Reading

Apurba Chatterjee, Department of Elderly Care, Royal Berkshire Hospital, Reading

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covid-19 norovirus