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Infectious Disease

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					           EPI 5240:
 Introduction to Epidemiology
  Gastroenteritis in Texas: an outbreak case-study
                     October 26, 2009




                    Dr. N. Birkett,
       Department of Epidemiology & Community
                       Medicine,
                University of Ottawa

16/10/08                                             1
                     Part 1
On the morning of March 11, the Texas
Department of Health (TDH) got a phone call from
a university student. He reported that he and his
roommate (who lived in a frat house) were
suffering from nausea, vomiting and diarrhea.
Both became ill during the night. Neither had seen
an MD.

They believed they were ill due to food eaten at a
local pizzeria the previous night. They wanted
advice about whether to take a biology mid-term
that afternoon.
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              Part 1 (Q’s)
• What questions would you ask the
  student?
• What advice would you provide?
• Do you think that this complaint should be
  investigated further?




16/10/08                                       3
              Part 2 (1)
Staff were skeptical, thinking students
wanted an excuse to miss the exam  but
decided to make a few calls.
•Pizzeria was closed until 1100,
•No answer at the student health centre




16/10/08                                  4
                      Part 2 (2)
• ER at hospital A revealed 23 university students
  had been seen for gastro in past 24 hours.
     – Only 3 similar patients seen from March 5-9, none
       from university
• 10:30, MD from Student Health Center called.
  20 cases of students with vomiting and diarrhea
  seen in previous day.
     – Normally, see only 1-2 similar patients per week.

Is this an outbreak at the university?

16/10/08                                                   5
                        Part 3
TDH visit hospital A that afternoon to review medical
records. Symptoms:
Vomiting:              91%
Diarrhea:              85%
Abdo cramps:           68%
Headaches:             66%
Muscle aches:          49%
Bloody diarrhea:        5%
Temperature:           98.8 to 102.4 (median 100)
CBC:                   elevated white cell count
Stool specimens:       pending
16/10/08                                                6
                       Part 3 (Q’s)
Broad categories of diseases to consider?

Infections
• Requires organism growth
      – Incubation period days, not hours
• Symptoms: diarrhea, nausea, vomiting, cramps. Can get
  fever and raised white count
Toxins
• Toxin already in food  disease in minutes to hours
• Symptoms: vomiting (**). Can include neurological
  symptoms
Pizza as source toxin.
Symptoms infection
16/10/08                                              7
                          Part 4
• Local hospitals asked to report any cases of
  vomiting/diarrhea seen in past week. Asked to
  collect stool samples on new cases.
• Preliminary cultures on 17 ill students were
  negative for 9 common bacterial causes of
  gastro, including:
     – Salmonella, shigella, E. Coli and Listeria


What do the negative stool culture results mean?

16/10/08                                            8
                 Part 6
Within 24 hrs, 75 persons with vomiting or
diarrhea had been reported to the TDH. All
were students from the university campus.
There were no cases among faculty, staff or
the local community. Median age was 19,
69% were freshmen and 62% were female.



16/10/08                                      9
                 Part 6 (Q’s)
• Is there anything else you would like to
  see from this preliminary data?
     – An epidemic curve!




16/10/08                                     10
           Epidemic curve, based on 75 cases




16/10/08                              Initial   11
                                      report
                         Part 6 (Q’s)
• Is there anything else you would like to see from
  this preliminary data?
     – An epidemic curve!
• How do you interpret the curve?
• What about the case on March 6?
• Next steps?
     – Contact university
           • What would need to be discussed?
     – Get more info
           • Case series interviews to generate hypotheses
              – Does the pizzeria hold up as a source?

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                   Part 7 (1)
• University is in small town (pop=27,354).
  Enrollment about 12,000. 2,386 live on
  campus in 36 residences.
• University has municipal water and
  sewage.
     – No breaks or work on water/sewage lines in
       past year
     – No recent road work or digging near campus

16/10/08                                            13
                             Part 7 (2)
• Two cafeterias on campus (run by same
  company) plus 6 fast-food places
     – 2000 students on food plan
     – Most on-campus students eat in main cafeteria
           • Hot entrees
           • Grill, deli bar and salad bar
     – Second cafeteria used by off-campus students and
       staff.
           • Hot entrees, grill and salad bar
           • No deli bar.
• Spring break starts in two days (March 13).
  Cafeteria will be closed for 10 days.

16/10/08                                                  14
                     Part 7 (3)
• Interview of 7 early cases revealed:
• 4 M; 3F. 6 freshmen;
     – 2 psych major,1 English/Animal husbandry major; 3
       undecided
• 5 different residence halls. All ate mainly in
  main cafeteria. All had eaten from deli bar; 2
  from salad bar and 3 from grill. No common
  food items were noted
• Only psych students shared any classes. 5 were
  in sorority/fraternity; 3 attended an ‘all school’
  mixer on March 6; 2 went to a Sci Fi film festival
  on March 7.
16/10/08                                                   15
                    Part 7 (Q’s)
• State your leading hypothesis on pathogen,
  mode of transmission, source and period of
  interest.
     – Viral infection
     – Food or beverage spread
     – Served at the main university cafeteria between
       March 5 and 10
     – Perhaps related to the Deli bar
• What actions would you take next?
     – Epi study with controls
     – Lab examination of foods (including ice)
     – Inspect operational methods; interview staff
16/10/08                                                 16
           Part 8 (environmental - 1)
• 31 staff work in cafeteria, 24 are foodhandlers.
     – 30 interviews. One person refused to participate (worked at the deli
       bar)
• Asked about responsibilities, which meals they served and where,
  use of gloves, hand washing practices, work schedule in key week
  and illnesses. They provided stool samples.
• No illnesses in staff.
• Deli Bar
     – Separate refrigerator and prep area.
     – Sandwiches made to order by foodhandler
     – New meat, cheese and condiments were added to partially depleted
       stock daily (leftover food items were not discarded first)
     – Food items were not refrigerated or kept on ice while deli was open
     – Containers were not routinely cleaned
• Deli Bar was closed by the Health Department on March 12.
     – Do you agree with this action?

16/10/08                                                                      17
                          Part 9 (epi)
• Need more information, including a control
  group
     – Options?
• Matched case-control study (done on March 12)
     – Case definition
           • Vomiting or diarrhea (3+ loose stools in a 24 hr period) with
             onset after March 5 in a university student seen at ER or the
             health centre. Had to be in dormitory during survey
     – Controls
           • Roommates of cases who did not become ill
     – Telephone interviews (why?)
     – 29 pairs of subjects

16/10/08                                                                 18
           Part 9 (epi – results)




16/10/08                            19
           Epidemic curve, based on 75 cases




16/10/08                       Exposure   Initial   20
                               window     report
                                Part 10
• By March 13, the outbreak had grown to include 125
  patients. CDC was invited to assist. They performed
  RT-PRC testing of stool samples for viruses.

• Unmatched case-control study done to explore source of
  infection.
      – Limited to students eating at main cafeteria
      – Case definition modified
            • Had to be member of university meal plan (need not be in
              residence)
      –    Controls were in meal plan but had not got ill.
      –    40 randomly selected cases
      –    160 controls
      –    Telephone interviews

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16/10/08   22
16/10/08   23
                        Final results (1)
• Water/ice negative for coliforms
• All stool cultures negative for bacteria
• 50% of fresh stool cultures on ill students were positive for Norwalk-
  like virus.
• Ham samples were positive for Norwalk-like virus (same DNA
  sequence as stool samples)
• Staff member who refused interview agree to provide information
     –     She sliced ham for three meals on March 9/10
     –     Prepared sandwiches on those days
     –     Wore gloves. Therefore, believed that hand washing didn’t matter.
     –     She wasn’t ill
     –     BUT her infant had watery diarrhea from March 7 to 10.
     –     The same Norwalk-like virus was found in her child’s stool
     –     Transmitted by contamination, not through infection



16/10/08                                                                       24
                   Summary
• What needs to be done to re-open deli
  bar?
     – Throw away all leftover deli bar food
     – Clean and disinfect all equipment and
       surfaces in deli bar
     – Require foodhandlers to submit stool sample
       prior to return to work? NOT NEEDED
     – Educate foodhandlers on proper procedures
     – Develop a sick foodhandler policy
16/10/08                                             25