Norovirus Outbreak in a Family Practice Center

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Norovirus Outbreak in a Family Practice Center

• Danae Bixler, MD, MPH

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. . . OR . . .

• Counting
• to Ten for
• Non-linear Thinkers.

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Objectives

• To describe
• An outbreak investigation in a family practice
  center
• An example of a cohort study
• 10 steps in outbreak investigation
• Epidemiology of Norvirus infections

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3/1/2001 Illness in 28 of 60 staff of a Family
Medicine Clinic

• Predominant symptom vomiting
• Onsets late PM of February 28 and early AM of
  March 1, 2001
• Physicians, nurses, residents
• Staff had eaten three meals in common
• Mon catered meal of Heavenly Ham
• Tue Mardi-Gras pot-luck
• Wed food from Subway

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Step 2 Establish the existence of an outbreak

• Occurrence of more cases of disease than expected
  in a given area or among a specific group of
  people over a particular period of time.

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Step 1 Prepare for Fieldwork

• Investigation
• Appropriate scientific knowledge, supplies,
  equipment

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Vomiting as a Chief Complaint

• Viral gastroenteritis
• Rotavirus (infant)
• Norovirus (older child / adult)
• Food poisoning due to pre-formed toxin
• Staphylococcus aureus
• Bacillus cereus
• Non-infectious (Sb, As, Cd, Cu, Fl, Zn, etc.)

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Incubation Periods for Suspect Infectious Agents
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Step 1 Prepare for Fieldwork

• Administration
• Make travel and coverage arrangements
• Consultation (roles)
• Collaboration on all steps (state / regional epi
  / LHD)

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Step 3 Verify the Diagnosis

• Through effort of the Regional Epidemiologist
• Routine stool cultures submitted through the
  hospital
• Stool for Norovirus submitted to the CDC

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Step 4 Establish a case definition and identify
and count cases

• 4a) Establish a case definition
• Initial case definition persons employed by or
  assigned to the Family Medicine Clinic who called
  in sick on March 1, 2001
• 4b) Identify and count cases
• Twenty-eight individuals were identified.

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Step 3, 5 and 6

• Verify diagnosis.
• Do descriptive epidemiology and develop
  hypotheses.

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Open-Ended Interviews (3/1/01) N10 persons who
called in sick

• Verify diagnosis
• Symptoms
• Sudden onset of profuse vomiting and diarrhea
• Systemic symptoms, including headache,
  arthralgias, myalgias, weakness
• Recovery (or near recovery)12 hours

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Open-Ended Interviews (3/1/01) N10 persons who
called in sick

• Descriptive Epidemiology
• Onset late on 2/28 early AM and morning of 3/1

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Open-Ended Interviews (3/1/01) N10 persons who
called in sick

• Hypothesis generation
• No common events outside of work
• Attendance at
• Monday luncheon (2/26) 3 (30)
• Mardi Gras pot luck (2/27) 10 (100)
• Wednesday lunch (2/28) 7 (70)

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Step 7 Evaluate hypotheses

• Regional epidemiologist obtained the menu for the
  Mardi Gras luncheon
• Questionnaire constructed (state)
• Interview of a convenience sample
• Recovered / well individuals on-site
• Local/ regional public health personnel
• Ill individuals by phone
• State staff

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Back to Step 4

• Case individual in attendance at the Mardi Gras
  luncheon (2/27/01) with illness characterized by
  vomiting or two or more episodes of diarrhea, and
  onset on or after February 28, 2001
• Control individual in attendance at the Mardi
  Gras luncheon with no symptoms of illness the
  week of 2/26/02.

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And Back to Steps 3 and 5 Verify the diagnosis
and perform descriptive epidemiology

• Interviews allow refinement of
• Descriptive epidemiology outbreak curve (time)
• Diagnosis

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Study Population

• 39 interviews
• Exclusions
• 1 person ill, but did not meet the case
  definition
• 1 did not attend the dinner
• 3 had onset prior to 2/28/02
• Final population N 34
• 16 cases
• 18 controls

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Characteristics of Illness (N16)

• Aches
• 10 (62)
• Chills
• 10 (62)
• Cramps
• 12 (75)
• Diarrhea
• 13 (72)
• Avg. 5.25 episodes

• Headache
• 11 (69)
• Nausea
• 13 (81)
• Vomiting
• 13 (83)
• Avg. 5.3 episodes
• Fever
• 4 (25)

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Step 1 Clinical Features in a Large
Community-based Outbreak of NLVCID, 200133622-8
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Step 7 RR of illness for the exposure candied
sweet potatoes 0.69 (95 CI 0.13 to 3.56)
p1.0)
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Step 7 RR of illness for the exposure chocolate
cake 0.97 95 CI 0.46 to 2.03) p0.78
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Step 7 RR of illness for the exposure seafood
jambalaya 1.45 95 CI 0.70 to 2.98) p0.50
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Step 7 RR of illness for the exposure Mardi
Gras punch 4.9 95 CI 1.32 to 18.25) p0.004)
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Step 8 Refine the hypothesis

• How could the punch have become contaminated?

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Other data

• Nursing home outbreak (same week)
• Onsets consistent with person-to-person spread
• Background illness
• Community
• Family Practice Center

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March 3, 2001 How was Mardi Gras punch made?

• Bottled grape juice
• Unsweetened canned pineapple juice
• Sprite
• Homemade ice rings
• Water
• Sliced fruit
• Doubloons
• Sliced fruit
• Mixed in bowl found on top of refrigerator

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Homemade Ice Rings

• Ice ring household A
• City water
• Person who made it had GI distress the day of
  the event

• Ice ring household B
• Well water
• All members of family of this household
  sequentially had similar illness over the
  previous month

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Step 9,10 Control Measures / Communication

• Contacted Regional Epidemiologist / Clinic
  Director March 3, 1030 AM
• Preliminary results of analysis suggest Mardi
  Gras Punch is the most likely culprit
• No evidence for contamination of commercial food
  product
• Recommend exclusion of ill persons and good
  handwashing

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Timeline

• Thursday, March 1, 2001
• Notification approximately 300 PM
• Open-ended interviews
• Study design
• Friday, March 2, 2001
• Interviews using a standard questionnaire
• Data entry
• Analysis completed 1030 PM
• Saturday, March 3, 2001
• Phone interview of persons who made the punch
  800 AM
• Preliminary results shared with the regional
  epidemiologist and clinic director 1030 AM

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Step 8 The lab gets the last word

• Environmental Specimen
• Water sample from kitchen tap of household B
• () total coliforms
• () E coli

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Step 8 The lab gets the last word

• Human Specimens
• 12 stool specimens
• Negative for Salmonella, Shigella, Yersinia and
  Campylobacter in the clinical laboratory
• 10 stool specimens
• PCR positive for NLV at CDC
• Identical nucleotide sequence

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Conclusion

• Mardi Gras punch was the source of an outbreak
  affecting approximately half the staff of a
  family medicine center
• Contamination likely introduced by
• Fecally-contaminated well water, OR
• Hands of one of the people who prepared the
  punch OR
• (possibly) residual environmental contamination
  in household B.

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Limitations

• Incomplete response rate on the cohort study

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Step 9 Implement control and prevention measures

• The well was taken out of service.

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Step 10 Communicate findings

• Written outbreak report distributed with
  laboratory results approximately one month later
  to
• LHD
• Clinic Director
• OLS
• Environmental Health
• Regional Epidemiologist
• CDC

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Step 1 The Minnesota ExperienceJID, 2000
181(Suppl 2)S281-S283

• 1981-1998, 295 foodborne outbreaks
• 120 (41) were due to Norwalk-like virus
• Definition median incubation period 24-48 hr,
  vomiting among gt50 of cases (or higher
  proportion of cases with vomiting than fever),
  and resolution of symptoms within 24-48 hr.
• 57 caused by major bacterial pathogens
• 33 (11) Salmonella
• 10 (3) Campylobacter jejuni
• 8 (3) E coli O157H7
• 6 (2) Shigella sonnei

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Characteristics of Norwalk-like viruses MMWR,
2001 50(No RR-9)
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Characteristics of Norwalk-like viruses MMWR,
2001 50(No RR-9)
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NLV - British Military Personnel Afghanistan,
May, 2002 MMWR, 2002 51477

• May 13-19 29 British soldiers / staff - Acute
  illness with
• Vomiting
• Diarrhea
• Fever
• Short incubation period
• Rapid recovery
• First three presented with severe illness
• 10 evacuated to England
• Lab diagnosis (England) NLV

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Conclusions

• NLV outbreaks are
• Good practice
• Important to investigate because of the total
  burden of disease
• Cause of significant disability and death,
  especially in vulnerable populations
• Challenging to investigate because laboratory
  diagnosis is not readily available

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Conclusions

• 10 steps of outbreak investigation
• Conceptual
• Provide a logical progression for the
  investigation
• Can / should be taken out of order (with caution)