NH Department of Health and Human ServicesDivision of Public Health Services

Norovirus Activity New Hampshire, 2006-2007

Beth Daly, MPH

Communicable Disease Epidemiologist

Communicable Disease Surveillance Section

NHICEP Meeting

March 13, 2007

NH Department of Health and Human ServicesDivision of Public Health Services

Viral Gastroenteritis

• Several viruses cause gastroenteritis– rotavirus, noroviruses, adenoviruses, sapoviruses, and

astroviruses

• Symptoms are often similar among etiologies, often unable to distinguish clinically

• CDC: each year 23 million cases of acute gastroenteritis are due to norovirus infection

• At least 50% of all foodborne outbreaks of gastroenteritis can be attributed to noroviruses

NH Department of Health and Human ServicesDivision of Public Health Services

Norovirus• Genus name of a group of of related, single-

stranded RNA, nonenveloped viruses • Member of the Caliciviridae family which includes

four viral genera: – Lagovirus, Vesivirus, Sapovirus, Norovirus

• Only sapovirus and norovirus can infect humans• Previously known as “Norwalk-like Viruses”• Norwalk virus is just one type of virus in the

Norovirus genus• Norwalk virus named for original strain which

caused an outbreak in Norwalk, Ohio in 1968

NH Department of Health and Human ServicesDivision of Public Health Services

Norovirus Genogroups• There are five norovirus genogroups

(divided into at least 31 genetic clusters)– Only 3 of these genogroups can infect humans

(GI, GII, GIV)– Genogroup GI: Norwalk virus, Southampton

virus, Desert Shield virus – Genogroup GII: Hawaii virus, Snow Mountain

agent, Toronto virus (GII/3) – Genogroup GIV: Ft. Lauderdale virus

NH Department of Health and Human ServicesDivision of Public Health Services

Clinical Presentation• Incubation period: 24-48 hours

– median in outbreaks 36 hours• Acute-onset:

– vomiting, watery non-bloody diarrhea, abdominal cramps, nausea

• Symptoms may vary based on genogroup • Dehydration most common complication• Results in reversible lesions in jejunum

– precise mechanism diarrhea and vomiting unknown • Symptoms last 24 to 60 hours • Recovery is complete and no evidence of serious long-

term effects• Asymptomatic in 30% of infections

– role in transmission unknown

NH Department of Health and Human ServicesDivision of Public Health Services

Transmission• Humans only known reservoir

– Some noroviruses present in swine, cattle, and mice, but these genogroups do not infect humans

• Transmitted primarily fecal-oral– consumption of contaminated food/water– direct person-to-person spread– Environmental/fomite contamination

• Good evidence exists for transmission due to aerosolization of vomitus – droplets contaminating surfaces or entering

oral mucosa and swallowed• Multiple routes seen in outbreaks

HANDS

AIR

ES

FOOD

H2O

NH Department of Health and Human ServicesDivision of Public Health Services

Transmission• Highly infectious

– As few as 10 viral particles may be sufficient for infection

• Viral shedding usually begins with onset of symptoms – Presymptomatic shedding may occur

• Shedding may continue for 2 weeks after recovery– Unclear to what extent viral shedding

72 hours after recovery signifies continued infectivity

NH Department of Health and Human ServicesDivision of Public Health Services

MMWR 2001; 50: RR-9

NH Department of Health and Human ServicesDivision of Public Health Services

Immunity• Immunity may be strain-specific • lasts only a few months• individuals are likely to be repeatedly

infected throughout their lifetimes. • Antibodies to the virus are noted

initially in young children ages 3 to 4• Antibody prevalence exceeds 50% by

age 50

NH Department of Health and Human ServicesDivision of Public Health Services

Immunity and Blood Type• Susceptibility to infection may be

genetically determined• People with blood group O at greatest risk

for severe infection• Noroviruses bind to several histo-blood

group antigens and different genogroups have differing affinity for ABO antigens

• GI noroviruses preferentially recognize blood group antigens A and O

• GII noroviruses preferentially recognize blood group antigens A and B

NH Department of Health and Human ServicesDivision of Public Health Services

Diagnosis•  RT-PCR detects norovirus RNA

– can be used to test stool and emesis samples• NH PHL requests stool

– Identification of virus can be best made from stool taken within 48 to 72 hours after onset• good results can be obtained on samples

taken as long as 5 days after onset• Virus can sometimes be found in stool

samples taken 2 weeks after recovery

NH Department of Health and Human ServicesDivision of Public Health Services

Epidemiology• CDC estimates 23 million cases of

norovirus each year in US• In NH, norovirus is not reportable• Outbreaks are reportable• What defines an outbreak?– Transmission within the facility?– Higher than normal number of cases?

NH Department of Health and Human ServicesDivision of Public Health Services

Reported Outbreaks of Viral Gastroenteritis, 2002-2007

Year Foodborne Person-to-person Total

2002 2 33 35

2003 1 29 30

2004 4 17 21

2005 3 16 19

2006 3 31 34

2007 YTD 0 46 46

Total 13 172 185

Note: Number of outbreaks includes all outbreaks with a suspect or confirmed viral etiology

YTD: as of 3/1/2007

NH Department of Health and Human ServicesDivision of Public Health Services

Reported Outbreaks of Viral Gastroenteritis, 2002-2007

05

101520253035404550

2002 2003 2004 2005 2006 2007 YTD

NH Department of Health and Human ServicesDivision of Public Health Services

2006-2007 Norovirus Season• Between December 1st-March 1st

– 64 outbreaks of norovirus/norovirus-like illness in institutional settings• 55 (86%) in longterm care facilities• 4 (6%) in acute care hospitals• 5 (8%) in schools

– 50 (78%) outbreaks submitted stool specimens• 25 (39%) met CDC criteria for a confirmed norovirus

outbreak (≥ 2 positive specimens)• 18 (28%) had one positive stool specimen

• Increase seen across the United States• CDC believes increase due to new strain

NH Department of Health and Human ServicesDivision of Public Health Services

Control- Public Health• Notify the NH DHHS Disease Control

Section immediately if you suspect an outbreak in your facility

• Follow NH DHHS Guidelines for Control of GI Outbreaks in Institutional Settings

• Collect stool specimens– Be sure to label lab requisition form with the

word “OUTBREAK” and your Facility Name– Also helpful if you could write name of NH

DHHS public health nurse you’re working with

NH Department of Health and Human ServicesDivision of Public Health Services

Control- Patient/Resident • Stop all group activities• Consider alternate ways of feeding the ill

to prevent them from dining in common areas

• Restrict/defer admission to affected areas for two incubation periods after last case

• Notify visitors and encourage handwashing during/after visits

NH Department of Health and Human ServicesDivision of Public Health Services

Control- Staffing Issues• Staff with GI symptoms should remain out of

work until 48 hours after symptom resolution• Exclude non-essential staff from affected areas • Interrupt movement of inter-department staff if

possible• Staff should frequently wash hands using soap

and water during suspect norovirus outbreaks• Use gloves and aprons whenever contacting an

affected individual or contaminated environment

NH Department of Health and Human ServicesDivision of Public Health Services

Control- Environmental• Noroviruses resistant to environmental challenge

– they are able to survive freezing– temperatures as high as 60°C– and have even been associated with illness after being

steamed in shellfish– can survive in up to 10 ppm chlorine well in excess of

levels routinely present in public water systems

• CDC recommends cleaning surfaces with 1000 ppm household bleach – equivalent to 5 tablespoons per gallon– Can other cleaners be used?

NH Department of Health and Human ServicesDivision of Public Health Services

What about Alcohol Based Hand Sanitizers?

• Attacks protein envelope of the virus

• Noroviruses are non-enveloped!

Lipid-protein envelope

Protein shell(capsid)

Nucleic acid genome(DNA or RNA)

20-300 nanometers diameter

NH Department of Health and Human ServicesDivision of Public Health Services

Thank you!

Questions/Comments?

Contact NH DHHS to report suspect outbreaks and to receive disease

control recommendations and supportOffice: 271-4496

After Hours: 800-852-3345 ext. 5300