A food-borne outbreak of gastroenteritis caused by norovirus GII in a university located in Guangzhou City, China

doi:10.21203/rs.3.rs-4647298/v1

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A food-borne outbreak of gastroenteritis caused by norovirus GII in a university located in Guangzhou City, China

https://doi.org/10.21203/rs.3.rs-4647298/v1

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In order to determine the causative pathogen and source of infection of an acute gastroenteritis outbreak in a university located in Guangzhou City, China, and summarize the lessons learned from food safety risk management.A series of epidemiological investigations were conducted in the university, including investigations of cases, food, drinking water, and the environment. A 1:4 matched case-control study was carried out to explore the risk factors for infection. Reverse transcriptase PCR was performed on all suspected cases for norovirus detection. Phylogenetic analysis was conducted to confirm pathogen typing. A total of 431 suspected cases were identified in this outbreak, of which 216 were laboratory-confirmed cases. The main clinical symptoms observed in the cases were diarrhea (62.6%) and vomiting (60.8%). A retrospective case-control study with a ratio of 1:4 was conducted. The results of multivariate analysis showed that four factors were significantly associated with the outbreak, including contact with patients' vomit or stool, presence of cases in the same dormitory, dining at Canteen B and Canteen E respectively. The odds ratios (OR) and their corresponding 95% confidence intervals (CI) for these factors were as follows: 15.587 (2.188 ~ 111.054), 3.166 (1.595 ~ 6.281), 3.86 (1.497 ~ 9.956), and 9.456(4.785 ~ 18.686), respectively. Phylogenetic analysis indicated that all eight specimens tested positive for norovirus GII.4 strains including seven confirmed outbreak cases and one food handler.Based on the environmental investigation, case-control study and laboratory test results, it was concluded that the outbreak was caused by kitchen workers infected by norovirus through contact. The health surveillance and hygiene practice of kitchen workers still need to be strengthened in the future.

Health sciences/Diseases

Health sciences/Gastroenterology

Health sciences/Risk factors

Food-borne Disease

Norovirus

Outbreak

Noroviruses (NoVs) are the leading cause of sporadic cases and outbreaks of viral acute gastroenteritis (AGE) across all age groups, accounting for nearly a fifth (18%) of all AGE cases and approximately 90% of viral gastroenteritis outbreaks and 50% of all-cause gastroenteritis outbreaks annually worldwide^1–3. In China NoVs are also main causes of AGE outbreaks in China, being implicated in 89% of outbreaks. However, despite no confirmation, they are often presumed to be the causative agent.⁴. Infection of NoVs is usually presented as nausea, vomiting, watery diarrhea and a self-limiting course lasting approximately 48–72 hours⁵. Severe complications and death are rare, but severe dehydration has been reported in some cases, especially among elderly, immunocompromised patients and pediatric cases⁶; ⁷. NoVs can primarily spread through the fecal-oral route, person-to-person contact or contaminated food, water, or fomites. The basic reproduction number ranges from 2.9 to 7.2⁸; ⁹. Due to their multiple modes of transmission and highly contagiousness, NoVs are the primary cause of outbreaks, particularly in semi-enclosed settings such as schools, hospitals, and nursing homes^10–12. Nearly 93.7% NoVs outbreaks occur in kindergartens and schools ,including primary schools, high schools and universities¹³.

NoVs are the predominant etiological agent responsible for foodborne diseases across the world. A comprehensive study estimated that NoVs were accountable for approximately 125 million cases (95% CI 70–251 million), establishing it as the primary causative factor behind foodborne illnesses.¹⁴. Food handlers are recognized as significant contributing factors in the transmission of NoV during foodborne outbreaks¹⁵; ¹⁶. The primary causative factor in many of these outbreaks is the contamination of food during preparation, predominantly occurring at the point of service by food handlers.¹⁷. In a South Korea study, it was found that approximately 18% of NoVs outbreaks during the study were related to asymptomatic food handlers, the detection rate of asymptomatic infection in winter was 2.2%, suggesting asymptomatic infected employees food handlers may be a potential transmission source in NoVs outbreaks¹⁸.

Guangzhou, the capital and largest city of Guangdong Province, is situated in Southern China. On November 25th, 2021, the Guangzhou Center for Disease Control and Prevention (GZCDC) received a notification regarding an outbreak of acute gastroenteritis characterized by sudden onset of diarrhea and vomiting among a significant number of students at a university in Guangzhou city. Preliminary investigation revealed a significant outbreak of AGE outbreak caused by NoVs, garnering extensive media and public attention. This investigation was conducted to determine the causative pathogen and source of infection, while also summarizing the specific characteristics and lessons learned from its management.

Settings

The university is a civilian-operated institution consisting of 7 academic colleges, encompassing a total of 242 classes, accommodating 15,378 students and employing 1,130 faculty members. Among the student population, approximately 98% (15226/15378) reside in on-campus dormitories where four students share each room. To cater to the dietary needs of the students, five canteens (Canteen A-E) are available on campus. Each canteen houses multiple distinct food stalls, resulting in a total of 83 food stalls managed by 347 food handlers.

The canteens B and E are operated by the same service provider, facilitating staff interchangeability between the two establishments, thereby enabling employees from canteen B to concurrently work at canteen E. Moreover, in response to students' work-study requirements, certain canteens employ temporary student workers. During the survey period, a total of 14 part-time student workers were hired at canteen E.

The Guangzhou Market Supervision Bureau mandates that canteens store food samples in a designated refrigerator for a duration of 48 hours. All students, canteen staff, and teachers on duty consume three meals daily at the campus canteen. No large-scale gatherings have taken place at the school within the four weeks preceding the outbreak.

Epidemiological investigation

This investigation was conducted from Nov 25th 2021 to Dec 6th 2021 at the university. The study population in the investigation of this outbreak comprised individuals who were suspected or confirmed cases. Suspected cases were defined as students, teachers, and other staff members (food handlers, cleaners, etc) in the university with at least one of the following two symptoms: 1) diarrhea ( ≧ three loose stools with in 24-hours); 2) vomiting more than twice within 24-hour period. Considering the date of onset of the first reported case and the longest incubation period of NoVs being 3 days, the search of the cases was carried out since November 20th,2021.Confirmed cases were defined as suspected cases that was positive for NoVs in feces or anal swab by reverse transcription polymerase chain reaction(RT-PCR). Cases were identified through a standardized self-administered questionnaires, and information on age, gender, occupation, class, dormitory, symptom onset time and clinical symptoms were collected. Information on demographic characteristics, symptoms, and post in kitchen for all food handlers in five canteens was also collected.

Case-control study

In order to find out the transmission mode and risk factors of this outbreak, a matched 1:4 case-control study was conducted by using a semi-structured questionnaire to gather information on suspected risk factors including demographic characteristics, symptoms, meals consumed in canteens, sources of drinking water, daily water consumption volume, history of contact with individuals exhibiting diarrhea and/or vomiting symptoms, as well as personal hygiene habits. For the case-control study, cases were selected from confirmed cases that developed symptoms of AGE on Nov 28, 2021 during the epidemic peak in the university. Age and gender-matched controls were selected from the students without any gastroenteritis-related symptoms. Considering that NoVs has an incubation period up to 3 days, controls were interviewed regarding potential exposures on November 26th to 28th,2021. Environmental hygiene investigation

The operations of the five canteens were evaluated by GZCDC working staffs, with specific focus on hand hygiene practices, food preparation and delivery procedures, tableware disinfection protocols, and recent employee health status. Environmental samples were collected from various locations including the food preparation station, cutting utensils, interior wall of the refrigerator, utensils storage area, meal break area, switches and doorknobs, public restroom, and sanitation room for Nov nucleic acid testing. Additionally, source and drinking water samples were collected. Water was tested for most probable numbers (MPN) of total coliform and Escherichia coli.

Laboratory investigation

Specimen collection

We collected fecal samples from all suspected cases with gastroenteritis symptoms. Samples for some early cases were tested for bacteria (Shigella, Campylobacter, Salmonella, Vibrio spp) by standard culture methods. No positive test results were obtained. Reverse transcriptase PCR (RT-PCR) for NoVs detection was performed for all the suspected case. We also collected stool specimens from all food handlers of the five canteens for NoVs testing. For highly transmissible environmental contagious agents, 139 specimens of common surfaces that spread pathogens through a rectal-oral route, such as doorknobs, toilets taps, kitchen rags, kitchen cabinet, cutlery, and taps of drinking water machine taps were collected on November 28,2021.

Nucleic acid testing

Fecal samples

Viral RNA extraction and amplification of partial RDRP and VP1 of NoVs 10% (wt/vol) fecal suspension was prepared with phosphate buffed saline (PBS) and clarified using centrifugation at 1500 × g for 20 min.

Environmental samples

Put the environmental swab into the nucleic acid extraction kit lysis buffer, and pressed the swab on the side wall of the EP tube to release the liquid in the swab. The steps of dipping and pressing the sidewall were repeated 3–4 times to ensure maximum virus release.

Nucleic acid extraction

Viral RNA was then extracted from clarified supernatant with a QIAamp MinElute Virus Spin kit(QIAGEN Inc.,Valencia,Calif) according to the manufacturers manual. The norovitus positive specimens by real-time RT-PCR were then genotyped for the RdRp and VP1 regions by using primer sets Mon431(5’-TGGACIAGRGGICCYAAYCA-3’) and G2SKR(5’-CCRCCNGCATRHCCRTTRTACAT-3’), yielding 560bp PCR products. A one step RT-PCR amplification reaction was performed by using the SuperScript ^TM OneStep RT-PCR with Platinum Taq(Invitrogen USA) according to the manufacturer’s instructions.

Phylogenetic analysis

The nucleotide sequence of the partial RdRp and VP1 was obtained by sequencing with abi 3100 Genetic Analyzer(Applied BioSystems,Foster City, CA,USA).The Sequences were genotyped using NoVs Typing Tool Version 2.0(https://www.rivm.nl/mpf/typingtool/norovirus). The phylogenetic trees were constructed using a neighbor-joining method after 1000 bootstrapping by using MEGA-X Software ( Mega Limited, Auckland, New Zealand).

Statistical analysis

Distributions of the major symptoms during the outbreaks were summarized using frequencies and proportions. Attack rates were calculated and compared using chi-square test between the two groups. Variables significant at p value < 0.05 in univariated analysis were included in an conditional logistic regression multivariate analysis model (the Wald test was introduced forward to screen variables). We calculated odds ratios (ORs) and 95% confidence intervals (CI) for the risk factors. P-values < 0.05 were considered as statistically significant. Analyses were performed using R 3.2.1 (The R Project for Statistical Computing, Vienna, Austria).

Descriptive epidemiology

A total of 431 suspected cases were identified in this outbreak, out of which 216 were laboratory-confirmed cases. Among the cases, students accounted for 98.38% (424/431), while there were 6 teachers and 1 kitchen staff member from Canteen B. The attack rate among students was 2.76%.

The main clinical symptoms of the cases were diarrhea (62.6%) and vomiting (60.8%). There were no cases of hospitalization or death (Table 1). 74.01% of the cases were male, and the median age of patients were 20 years old. The outbreak lasted 14 days from 23 November to 6 December. The peak incidence was observed on 28 November, with the initial case reported on 23 November, while the highest number of cases occurred between 26 November and 1 December. (Fig. 1). The vast majority of students are residential. Cases were found in all 8 dormitory buildings, and the number of cases in dormitory NO.10 was the largest, accounting for 32.55% (138/424) of all student cases, followed by dormitory NO.9, accounting for 24.76% (105/424) of all student cases(Table 2). All the seven colleges have cases. The highest attack rate was found in the college of Health (4.79%) and the College of Architecture and Engineering (3.59%).(Table 3)

Table 1

Distribution of clinical symptoms of 431 cases
Symptom	Number of cases	The proportion of composition (%)
Diarrhea	270	62.6
Vomiting	262	60.8
Nausea	216	50.1
Fever	205	47.6
Abdominal pain	196	45.5

Figure 1. Temporal distribution of onset in this outbreak

Table 2

Distribution of dormitory buildings for 424 student
Dormitory building number	Number of the students	Cases	Attack rate(%)
NO.6	2462	88	3.6
NO.10	4481	138	3.1
NO.9	3698	105	2.8
NO.5	527	14	2.7
NO.1	1929	47	2.4
NO.4	494	12	2.4
NO.2	916	13	1.4
NO.7	719	6	0.8
Total	15226	423	2.8

*Note: The university has a total of 10 dormitory buildings, of which the 8th is an isolated dormitory, which is not occupied at ordinary times. Only one person lived in the third building, and the disease occurred.

Table 3

Department distribution of cases of 424 cases
Name of college	Number of students	Number of cases	Attack rate(%)
Department of Health	313	15	4.79
Department of construction engineering	2118	76	3.59
Department of art media	2161	68	3.15
Department of automation engineering	1151	31	2.69
Department of information engineering	4252	124	2.92
Department of foreign Languages and foreign Trade	1804	38	2.11
Department of economics and management	3579	72	2.01
Total	15378	424	2.76
*Due to the fact that some students do not live on campus, the total number of students counted here is slightly different from the total number based on dormitory accommodation

The investigation conducted among the food handlers revealed that the initial case involved a kitchen staff member working in canteen E, who exhibited symptoms of diarrhea on November 23rd but continued to work, and had previously worked in canteen B. Six food handlers worked in Canteen E reported mild gastrointestinal discomfort during 24th to 25th. Out of the remaining 14 part-time students, eight developed symptoms, resulting in an attack rate of 57.14% in part-time students.

Environmental hygiene investigation

Each of the food stalls operated independently with different types of food. There is no high-risky food provided in each stall. The operation mode is outsourcing bidding system. In canteen E, the sanitary conditions were poor in some stalls, and the processed food arranged disorderly, the read-to-eat food randomly placed on the shelf es closed to the ground. Furthermore, after disinfection, tableware is stored outdoors in the canteen, posing a risk of contamination.

The college provides piped, chlorinated water throughout the campus, while qualified companies supply bottled water for drinking purposes in the dormitories and teaching buildings on each floor. The scheduled testing reports for tap water showed that the water quality met the requirements.There was no difference between students and teachers drinking and using water.

Laboratory inspection

The NoVs was detected in 216 cases, with a positive rate of 50.11% among the affected individuals.The nucleic acid of NoVs was tested in all 347 kitchen workers, and a total of 57 individuals (16.42%) were found positive. However, while the symptoms exhibited by the initial case aligned with clinical presentations of NoVs, the symptoms observed in other workers were atypical.

Totally 139 environmental samples were collected from various locations at the university, including the food preparation station, cutting utensils,drinking water, refrigerator interior, utensils, utensil storage area, meal break area, switches and doorknobs, public restroom, and sanitation room. The total number of specimens collected from each location were 39, 13, 12, 12, 12, 12, 12, 12, 11, and 4. Notably, all samples tested negative for NoVs nucleic acid detection. Five water samples collected from the kitchen of Canteen A-E, and one samples from dormitory NO.10 were all tested negative for total coliforms, fecal coliforms.

Phylogenetic analysis

Eight sequences with a 560 bp size fragment on the RdRP and Vp1 regions were obtained by sequencing (5 confirmed outbreak cases, 3 food handler), and phylogenetic analysis showed that they all belonged to NoV GII.4 [P31]. The nucleotide sequence identitity values among 8 strains had a range of 99.8%~100%(data not shown), which had a close relationship with ID/2015/GII.Pe-GII.4-Sydney-2012/Y-024(MK408523) (Fig. 2–3).

Figure 2. Phylogenetic analysis of GII noroviruses based on partial RdRp gene

Figure 3. Phylogenetic analysis of GII noroviruses based on partial VP1 gene

Risk factors for the outbreak

The early cases with the onset date of November 25 to 27 were analyzed. Taking the onset cases as the case group (n = 95), with gender and college as the matching factors, and taking the contact history 72 hours before the onset, dining place 72 hours before the onset, drinking water and hygiene habits as the influencing factors, a 1:4 retrospective case-control study was conducted. The results showed that in univariate analysis, 7 factors were related to the occurrence of the disease. then,the seven related factors were included in the multivariate analysis model. Four factors were still related with the outbreaks: contact with patients’ vomit or stool, cases appeared in the same dormitory, dining in Canteen B, and dining in Canteen E, respectively. The OR and 95%CI were 15.587(2.188 ~ 111.054),3.166༈1.595 ~ 6.281), 3.86༈1.497 ~ 9.956) and 9.456༈4.785 ~ 18.686), respectively.(Table 4)

Table 4

Result of 1:4 retrospective case-control study of early onset cases
Variable		Case group (N = 95)	Control group (N = 380)	Univariate analysis		Multivariate analysis
Variable		Case group (N = 95)	Control group (N = 380)	OR(95%CI)	P	OR(95%CI)	P
History of exposure 72h before survey	Contact with cases	13(13.68)	15(3.95)	4.063(1.799 ~ 9.177)	0.001
	Contact with patients’ vomit or stool	4(4.21)	2(0.53)	8.000(1.465 ~ 43.677)	0.016	15.587(2.188 ~ 111.054)	0.006
	Cases appeared in the same dormitory	29(30.53)	41(10.79)	3.936(2.216 ~ 6.989)	0.000	3.166(1.595 ~ 6.281)	0.001
Dining place 72h before survey	Canteen A	19(20.00)	53(13.95)	1.722(0.895 ~ 3.313)	0.103
	Canteen B	14(14.74)	22(5.79)	2.996(1.42 ~ 6.321)	0.004	3.860(1.497 ~ 9.956)	0.005
	Canteen C	18(18.95)	60(15.79)	1.277(0.691 ~ 2.362)	0.436
	Canteen D	27(28.42)	73(19.21)	1.752(1.019 ~ 3.010)	0.042
	Canteen E	74(77.89)	129(33.95)	7.962(4.391 ~ 14.437)	0.000	9.456(4.785 ~ 18.686)	0.000
Drinking water	Source of drinking water
	Tapped	17(17.89)	94(24.74)	0.412(0.21 ~ 0.81)	0.010
	barrelled water	30(31.58)	126(33.16)	0.58(0.331 ~ 1.015)	0.056
	direct drinking water	15(15.79)	52(13.68)	0.667(0.324 ~ 1.372)	0.271
	running water	32(33.68)	75(19.74)	1.000	-
Health habit	Wash hands before dinner
	Never	2(2.11)	5(1.32)	1.000	-
	At every turn	49(51.58)	247(65)	0.472(0.089 ~ 2.495)	0.377
	Once in a while	14(14.74)	45(11.84)	0.754(0.137 ~ 4.154)	0.745
	Sometimes	30(31.58)	83(21.84)	0.82(0.153 ~ 4.387)	0.816
	Wash hands after using the toilet
	Never	1(1.05)	2(0.53)	1.000	-
	At every turn	92(96.84)	355(93.42)	0.552(0.05 ~ 6.118)	0.628
	Once in a while	2(2.11)	5(1.32)	0.883(0.048 ~ 16.232)	0.933
	Sometimes	0(0.00)	18(4.74)		0.971
	Wash hands with hand sanitizer or soap
	Never	8(8.42)	28(7.37)	1.000	-
	At every turn	25(26.32)	167(43.95)	0.546(0.23 ~ 1.298)	0.171
	Once in a while	44(46.32)	131(34.47)	1.22(0.523 ~ 2.85)	0.645
	Sometimes	18(18.95)	54(14.21)	1.209(0.477 ~ 3.061)	0.689
	The length of washing time
	< 10 seconds	40(42.11)	163(42.89)	1.000	-
	10–20 seconds	48(50.53)	154(40.53)	1.273(0.793 ~ 2.044)	0.317
	> 20 seconds	7(7.37)	63(16.58)	0.466(0.2 ~ 1.084)	0.076

Control measures

The following control measures were taken: 1)Suspected and confirmed cases were isolated until 72 h after the symptoms disappeared. 2)Reinforcement of hand hygiene, all students and teachers were asked to wash their hands and to wear masks while enter canteen during the period of outbreak. 3)Environment disinfection. The university conducted environmental disinfection three times a day during the period of the outbreak, including dormitory, academic buildings, canteens and etc. Instruments and the facility were thoroughly cleaned and disinfected, and air in the classroom was ventilated timely. 4)Re-education of food handling safety for all food handlers and asymptomatic food handlers were required to isolated until the NoVs were tested negative for twice (interval of 1 day). After a week of environment surveillance, searching and isolation of infectious cases, including both symptomatic and asymptomatic individuals, and thorough disinfection of the campus, this outbreak ended, and no new case occurred after December 7th.

In this investigation, we reported an outbreak of NoVs in Guangzhou, which was the first publicly documented GII.4 Sydney [P31] AGE outbreaks in Southern China. The epidemic curve with a sharp upward slope and a gradual downward slope suggested a point source outbreak and further propagated by person-to-person transmission, which have been also reported especially in relatively closed settings¹⁹; ²⁰. The entire campus used the same municipal tap water and drinking water, and all laboratory tests were up to standard; therefore, water source factors could be excluded. Multiple lines of evidence substantiate that the origin of this outbreak may be attributed to food handlers infected in Canteen E. Firstly, the epidemic curve and distribution suggested it is a common source outbreak followed by the secondary transmission with in dormitory or class. Secondly, case-control study suggested that eating at canteen E was the risk factors for NoVs infection. Thirdly, the asymptomatic infection rate in food handlers was high and samples obtained from food handlers and students cases were positive for NoVs GII.4. They showed 100% sequence homology in phylogenetic analysis. Lastly, more than 20% dormitory has reported 2 cases and more, and the time interval of onset of AGE was about 2-3days, which indicated person-to-person transmission in the middle and late stage of the outbreak. The outbreak was quickly managed after isolated asymptomatic food handlers and cases and implementation of thorough disinfection, which corroborated the judgment of food-borne and contact transmission in the outbreak.

Food-borne transmission is one of the major routes of NoVs outbreaks. In our investigation, the asymptomatic food handlers were the most likely source of infection. Although the role of asymptomatic food handlers in outbreaks is unclear, there is mounting evidence that asymptomatic food handlers have been reported as the source of NV outbreaks²¹[17, 20]. In a study by Sabrià et al, food handlers involved in gastroenteritis outbreaks were sampled, and it was found that 59.1% of food handlers were shedding NoVs. Furthermore,70% of these handlers were classified as asymptomatic²². Some laboratory studies and outbreak investigations detected the presence of NoVs RNA on the hands of food handlers, which demonstrated the feasibility of NoVs transmission through virus-shedding food handlers²³; ²⁴. Ozawa and Sabrià compared the mean viral loads of symptomatic and asymptomatic individuals found that the mean viral loads of NoVs among asymptomatic individuals are similar to those of symptomatic individuals²²; ²⁵. In this investigation, we analyzed samples from all food handlers, the asymptotic infection rate was 16.42%. The contamination likely occurred through the contamination of food or indirectly via contaminated food preparation surfaces or utensils. Although recommended by the local CDC, practices such as using gloves when preparing ready-to-eat food were not consistently observed, even when workers were aware of the necessity to do so. Additionally, some food handlers may exhibit mild symptoms (such as abdominal discomfort or occasional loose stools within a 24-hour period) prior to an outbreak without realizing that they might be ill and therefore fail to request sick leave. The failure to report in a timely manner could be attributed to inadequate training. Mclntyre et al. discovered that food safety trained food handlers exhibited significantly enhanced hand washing practices and attitudes in comparison to the untrained group of food handlers.²⁶.Considering the crucial role of food handling in preventing NoVs infections, it is imperative to advise food handlers to adhere to stringent hygiene practices within the kitchen environment. Furthermore, regular and periodic training sessions should be conducted for all staff members, particularly during enterovirus epidemic seasons.

In certain regions, the implemented strategies for preventing foodborne infections involved prohibiting food handlers with diarrhoea from working until 48–72 hours after achieving asymptomatic status.²⁷ However, due to the occurrence of prodromal and asymptomatic shedding, there is a potential for both symptomatic and asymptomatic individuals to contaminate the workplace. An evaluation study revealed that the implementation of these recommended measures resulted in a reduction of transmission by only 85%²⁸. In the present outbreak, in order to control the outbreak, the infected food handlers should only return to work after two consecutive stool specimens collected at 1-day intervals test negative for NoVs. After the implementation of measures such as closure of high-risk stalls, isolation of canteen food handlers with NoVs positive, and thorough disinfection of canteen, the outbreak quickly subsided, which further confirmed the hypothesis that food handler contamination in the canteen B was the root cause of the outbreak.

All GII.4 sequences in this outbreak belonged to GII.4 Sydney 2012 [P31], which emerged in 2012 and caused outbreaks during the 2012–2013 season^29–31. A study analyzed NoVs outbreaks in China between October 2016 to December 2020 found that GII.4 Sydney [P31] accounted for 6.19% among the GII outbreaks¹³. GII.4 Sydney[P31] have been continuously detected in outbreak surveillance³²; ³³. Zhu et al’s study suggested that GII.4 Sydney [P31] was undergoing evolution were likely to able escape the pressure of population immunity and cause a global epidemic of NoVs once again. Therefore, the monitoring of GII.4 Sydney strain is important for potentially emerging GII.4 variants¹³.

Limitations

There were also some limitations in this study.Firstly, only high-risk canteens was investigated and we could not determine the specific contamination sources by food handlers. Most cases cannot remember whether they had eaten certain foods or not, which makes it impossible to analyze key control links in food processing and storage. Secondly, the delay in conducting the survey, 1 week after the incident, which may have resulted in recall bias for some factors and misclassification bias. Finally, some canteen employees may have failed to disclose any symptoms of gastroenteritis to the investigation team due to fear of adverse consequences, but this information was important to further trace the source.

Our survey showed that food handlers were infected with NoVs and transmission may have been possible due to unhygienic practices. The consumption of food or drink by students at canteen B and E was determined as the probable cause of the outbreak. Our results also indicate that it is necessary to analyze stool samples from all food handlers, especially those who are asymptomatic, during outbreaks of NoVs gastroenteritis. Epidemiological investigation proved to be useful in determining the probable source of infection and implementing timely intervention measures.To prevent AGE outbreak associated with NoVs, food handlers should take daily check-ups and undergo periodic food safety training.

Ethical approval and consent to participate

Informed consent have been list at the beginning of the standardized questionnaire, verbal consent was obtained by the principal investigators through a face-to-face conversation with the students,teachers and food handlers witnessed by the CDC working staff. The investigation and experiments were performed in accordance with the relevant guidelines and regulations and approved by the Ethical Committee of Guangzhou Center for Disease Control and Prevention (GZCDC-ECHR-2024P0081).

Competing interests

The authors declare no conflict of interest.

Funding

This research was supported by Key medical discipline of Guangzhou (2021-2023-11) and Guangzhou Science and Technology Program key projects (grant nos. 2023A03J0939 and 2024A03J0368 ).

Author Contribution

All of the authors contributed significantly to the research.Wang Hui, Xie Huaping and Li Xiaoning wrote the main manuscript text, Li Xiaoning and Xie Huaping prepared figures 1-3.Chen Changming, Zhen Ruonan, Lu Jianyun conducted the investigation and data analysis. All authors reviewed the manuscript.

Acknowledgement

We thank Guangzhou Municipal Administration of Market Supervision for regularly providing data, and we acknowledge the staff of the Guangzhou centralized supervision warehouse and all participants in this study.

Data Availability

The datasets used and analyzed during the current study available from the corresponding author on reasonable request. with the permission of GZCDC.

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No competing interests reported.

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A food-borne outbreak of gastroenteritis caused by norovirus GII in a university located in Guangzhou City, China

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Abstract

Figures

Introduction

Materials and Methods

Settings

Epidemiological investigation

Case-control study

Laboratory investigation

Specimen collection

Nucleic acid testing

Fecal samples

Environmental samples

Nucleic acid extraction

Phylogenetic analysis

Statistical analysis

Results

Descriptive epidemiology

Environmental hygiene investigation

Laboratory inspection

Phylogenetic analysis

Risk factors for the outbreak

Control measures

Discussion

Limitations

Conclusion

Declarations

Ethical approval and consent to participate

Competing interests

Funding

Author Contribution

Acknowledgement

Data Availability

References

Additional Declarations

Status:

Version 1