Connecticut Epidemiologist Newsletter   •  September 2023   •   Volume 43, No 6

School Norovirus Outbreak in Connecticut 2023

Background

Norovirus, a highly contagious virus, is the most common cause of vomiting and diarrhea from acute gastroenteritis in the United States (1). Norovirus is spread via the fecal-oral route and is extremely contagious because only a small number of infectious particles can make someone ill. The virus can remain infectious on surfaces and objects for up to two weeks and is resistant to many common disinfectants (2). Norovirus outbreaks commonly occur in schools and other congregate settings, causing absences, interruptions in operations, and logistical challenges. Local health departments play a key role in outbreak investigation and management

On February 9, 2023, a local health department (LHD) was notified of a potential outbreak at a Connecticut school in their district. Initially, the LHD was notified of several students and staff experiencing gastrointestinal illness (GI) including nausea, vomiting, and diarrhea. The LHD received notification of additional cases in the following days.  

Staff at the LHD worked with the school to investigate the outbreak and implement infection control and prevention measures. This article summarizes actions taken including collecting case reports, conducting an environmental assessment, interviewing food service workers (FSWs), collecting stool specimens, and providing recommendations for mitigation strategies.  

Epidemiological Investigation

The school nurse collected epidemiologic data from students and non-FSW staff that reported GI illness. Case information included name, grade/staff role, symptoms, and onset and resolve dates/times. A case was defined as an individual experiencing vomiting and/or diarrhea who worked at or attended the school during the outbreak period.  

A total of 164 people reported illness including 127 students and 39 staff. The outbreak resulted in an overall attack rate of 25.3% of students and 35.5% of staff. Cases were reported from all grades (6 – 12) as well as from staff in multiple departments. Primary clinical manifestations included vomiting (n=122 [74% of cases]), diarrhea (n=85 [52%]), and abdominal cramps (n=22 [13%]). The mean duration of illness was 20.6 hours (range 4 – 96 hours). Reported symptoms and duration of illness indicated probable norovirus infection. Although no single exposure was identified, the epidemiologic curve suggested a possible point-source exposure due to a large number of cases reported over a 3-day period. [Figure 1]

Environmental Investigation and Control Measures

The LHD performed an environmental investigation of the school dining facilities. Proper glove use and hand washing was noted. Signage about what to do when ill was not provided in all languages used by FSWs.  A student was observed eating chips with bare hands out of a communal bowl. In response, self-serve dining options were immediately interrupted and provision of pre-packaged, single-serve items, including sandwiches, salads, and bags of chips, were implemented.  

Local health department staff interviewed all eight FSWs using a food employee interview form. Three FSWs reported experiencing symptoms of vomiting and diarrhea with symptom onset dates of 2/10/23, 2/16/23, and 2/28/23. No FSWs reported working while ill. Stool specimen collection kits were distributed to and collected from three FSWs (two symptomatic, one previously symptomatic but asymptomatic at time of collection). The LHD provided food service management with advice on best practices for food safety and preventing transmission of foodborne illness. Additional training on hand hygiene was provided by management.  

Investigation of routine cleaning practices prior to the outbreak found them to be insufficient to effectively reduce transmission due to use of disinfectant that was not effective against norovirus and inadequate frequency of disinfection. The school hired a third-party cleaning company for enhanced environmental cleaning with a Food and Drug Administration (FDA) approved disinfectant effective against norovirus multiple times per day following report of the outbreak. The school closed for deep cleaning the day after reporting the outbreak to the LHD.  

Control measures recommended by the LHD and implemented by the school included increased environmental cleaning; exclusion of ill persons for at least 48 hours after symptoms ceased; restriction of extracurricular group activities and events including rehearsals, sporting events, and team dinners; education on hand hygiene; posting signage about what to do when ill for FSWs in appropriate languages; and modifications to dining hall operations. 

 

Laboratory Investigation

Stool specimens collected from three FSWs, one staff member, and three students were tested at the DPH State Public Health Laboratory (SPHL). Among collected specimens, five (71%) tested positive for Norovirus Genotype I by reverse transcription polymerase chain reaction (RT-PCR). Sequence analysis was conducted on the five positive specimens by the Wadsworth Center Laboratory in New York. Four of the samples were identified as GI.3[P13]. Genotype could not be determined for the remaining sample. 

Discussion

The investigation indicated that the outbreak was cause by norovirus. The strain of norovirus identified from genotype sequencing (GI.3[P13]) was seen in 5% of all norovirus outbreaks reported to CaliciNet, a national norovirus outbreak surveillance network,  from September 2022 through February 2023 (3). When a norovirus outbreak occurs in a congregate setting, prompt notification and implementation of stringent prevention and control efforts is necessary to reduce the incidence of illness and duration of an outbreak. Education is essential to decrease transmission and risk of illness. To prevent norovirus outbreaks, it is important to stay home when ill, wash hands with soap and water, properly disinfect after bouts of vomiting or diarrhea, and avoid preparing food for others when ill (4).

Reported by

Local Health Department Staff

Acknowledgements

We thank the school nurse for diligence in collecting case report information and communication. We also thank the Connecticut Department of Public Health for their guidance and support.

References

1. Centers for Disease Control and Prevention. (2021, March 5). Burden of norovirus illness in the U.S. Centers for Disease Control and Prevention. Retrieved April 17, 2023, from https://www.cdc.gov/norovirus/trends-outbreaks/burden-US.html

2. Centers for Disease Control and Prevention. (2021, March 5). About Norovirus. Centers for Disease Control and Prevention. Retrieved April 17, 2023, from https://www.cdc.gov/norovirus/about/index.html

3. Centers for Disease Control and Prevention. (2023). Norovirus US Outbreak Map: CalciNet. Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/norovirus/reporting/calicinet/data.html  

4. Centers for Disease Control and Prevention. (2022, November 28). Preventing Norovirus. Centers for Disease Control and Prevention. Retrieved April 17, 2023, from https://www.cdc.gov/norovirus/about/prevention.html

 

 

This page last updated 10/05/2023