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Name(s):____________________________ Team number:_____________________ School:____________________________ Disease Detectives division B Mentor Invitational 2008 Total points______/ 85 Matching Correctly match the following epidemiological terms in the left hand column with the appropriate description, example or formula in the right hand column. Choose the best answer. (2 points each) 1.____vehicle A. habitat where the infectious agent normally lives, grows, and multiplies 2.____prevalence B. any mode or mechanism by which an infectious agent is spread to a susceptible host 3.____endemic C. a person without apparent disease who is nonetheless capable of transmitting the disease to others 4.____carriers D. constant low frequency of disease 5.____transmission E. acquired in a hospital 6.____vector F. infectious diseases that are transmissible under normal conditions from animals to humans 7.____epidemiology G. disease occurring in a population at a higher than normal frequency 8.____surveillance H. an epidemic which spreads over several countries or continents and affects a large number of people 9.____reservoir I. objects such as food, water, biological products and fomites that may directly transmit an infectious agent from a reservoir to a host. 10.____nosocomial J. the number or proportion of cases/events/conditions in a given population at a given time 11.____zoonoses K. science concerned with the distribution and determinants of health events in human populations 12.___epidemic L. the systematic, ongoing collection, analysis, interpretation, and dissemination of health data 13.___incidence M. various arthropods that transmit pathogenic organism from one host to another 14.____mortality rate N. number of new cases during a period divided by the total population 15. ____ pandemic O. deaths per total infected Page 1 Norovirus Outbreak in an Elementary School --- District of Columbia, February 2007 On February 8, 2007, the District of Columbia Department of Health (DCDOH) was notified of an outbreak of acute gastroenteritis in an elementary school (prekindergarten through sixth grade). The school nurse reported that 27 students and two staff members had become ill during February 4--8 with nausea, vomiting, and diarrhea; because symptoms lasted <48 hours, a viral etiology was suspected. Epidemiologic Investigation On February 9, DCDOH conducted a site visit and interviewed school personnel to determine the possible etiology of and risk factors for illness and to recommend additional control measures. The school had two to three classes per grade, and one to three staff members were assigned to each class. Although students attended a few classes outside their classroom each day (e.g., art or math), they spent the majority of time in their own classrooms. No outbreaks of gastrointestinal illness in the community were reported to DCDOH during this period. A questionnaire was developed to use in a cohort study of all staff members and students. Because no food was served at the school other than lunches that students brought from home and prepackaged snacks served in prekindergarten classes, foodborne transmission was not suspected; questions focused on illness onset, symptoms, school grade, classroom, special classes (e.g., art), ill contacts, and use of certain facilities or equipment (e.g., library computers) or participation in certain programs (e.g., after-school programs). Questionnaires were sent home by the school principal with all staff members and students the afternoon of February 9. The school nurse identified additional cases beginning February 9 by visiting each classroom daily; she interviewed persons who became ill during school and interviewed absent ill persons or a family member by telephone regarding grade, classes, illness onset, and symptoms. Information regarding ill contacts, facility and equipment use, and participation in programs was unavailable from the participants enrolled by the nurse. Of 314 students and 66 staff members at the school, 207 students and 59 staff members participated in the DCDOH investigation, for a total of 266 participants. Of 266 participants, 103 met the case definition. Among the 103 ill persons, 79 were students and 24 were staff members. Reported symptoms included vomiting (64%), nausea (56%), and diarrhea (47%). The median duration of illness was 36 hours (range: 0.2 to 96 hours). Median length of stay at home after onset of symptoms was 1 day (range: 0--4 days). Page 2 16. Write a case definition for this outbreak. (5 points) 17. Calculate the overall attack rate for those meeting the case definition. Round to the nearest percentage. (3 points) 18. What percentage of the ill persons were students? (3 points) 19. What percentage of the ill persons were staff members? (3 points) Laboratory Investigation Stool-specimen collection kits were provided during the DCDOH site visit on February 9, and specimens were received from two ill persons. Twenty-five swabs were used to sample environmental surfaces. Although February 9 was the day after the initial bleach cleaning, several surfaces had not been cleaned and were visibly soiled. Sampled surfaces included toilets, faucets, water fountains, doorknobs, mice and keyboards from three computers (each in a different room), school utensils, and toys. Samples were tested by reverse transcription--polymerase chain reaction (RT-PCR) for norovirus and DNA sequencing; stool specimens also were cultured for bacteria. Laboratory results were available February 13. One (4%) of the 25 environmental swabs, from a computer mouse and keyboard in first-grade classroom J, was positive for norovirus subtype GII. Norovirus subtype GII also was identified in both stool specimens. Noroviruses from the two stool specimens and a single environmental sample were identical by DNA sequencing of region B, the gene commonly used for genetic classification. Bacterial cultures of stool specimens and environmental samples were negative. Page 3 20. Based on the laboratory data, as noted above, what interventions would you recommend to control this outbreak? (5 points) 21. Development of protective antibodies in a potential host through response to infection or immunization. (1 point) A. Herd immunity B. Active immunity C. Passive immunity D. None of the above Page 4 True or False (2 points each) 22._____ A cohort study is used in an outbreak setting when a complete list of participants is available. 23. _____ The measure of risk used in a cohort study is the odds ratio. 24. _____ A cross-sectional study is basically the same as a survey. They are good for examining the relationship between a variable and a disease, not for determining cause and effect. 25. _____Latency period is the period of time from exposure to the onset of symptoms. 26._____ A pathogen is an organism that is never found on a healthy person. 27. _____ The single most important way to stop the spread of infection or disease is by performing good hand hygiene. 28. With most new infectious diseases, some human action is involved that changes the environment so that an existing microbe may take up residence in a new niche. Once that happens, a pathogen that had been confined to a remote habitat appears in a new or wider region, or a microbe that had infected only animals suddenly begins causing human disease. List two human activities/actions that may have led to the emergence and spread of new diseases. (6 points) 29. A ____ case has many factors that point to a diagnosis but may lack lab verification. (1 point) A. B. C. D. Confirmed Probable Possible None of the above Page 5 30. List the three main components to the epidemiologic triad. (3 points) 31. Antibiotics may be used to treat this type of pathogen. (1 point) A. B. C. D. E. Virus Prion Bacteria A and B All of the above 32. Disease prevention is the key to public health. It is always better to prevent a disease than to treat it. Vaccines prevent disease in the people who receive them and protect those who come into contact with unvaccinated individuals. Vaccines help prevent infectious diseases and save lives. Vaccines are responsible for the control of many infectious diseases that were once common in this country. (5 points) List 5 vaccine preventable diseases. 33. An epidemic curve: (1 point) A. B. C. D. E. graphically displays the scope of an outbreak shows the number of people affected by an outbreak shows the course of the outbreak over time all of the above A and B Page 6 34. An outbreak of diarrhea in a flood-hit city in central Mozambique has claimed the lives of 64 people since early January 2008, the local council said on Tuesday [5 Feb 2008]. The municipal authority in the city of Tete said that a total of 835 people had contracted diarrhea from contaminated water since the flooding began at the start of 2008. "64 of that total have not survived," the council's statement said. What is the case fatality rate? Show the formula. (3 points) Calculate the odds ratio given the following data. Ill Ate watermelon Did not eat watermelon Total Yes 72 115 187 No 5 122 127 77 237 314 Total 35. What was the odds ratio of persons who ate watermelon and becoming ill? (3 points) A. 8 B. 15 C. 800 D. 62 Page 7 Tie Breaker #1 Match each disease with the causative agent (one point each) Disease Causative agent 36. _______________Lyme disease Bacterium 37. _______________Smallpox Virus 38. _______________Anthrax Parasite 39. _______________Giardiasis Prion 40. _______________Legionnaires disease Unknown 41. _______________Trichinosis 42. _______________Rabies 43._______________Dengue fever 44._______________Chagas disease 45. ______________Creutzfeldt-Jakob 46. ______________Tuberculosis 47. ______________Kawasaki disease Page 8 Tie breaker #2 48. List the 10 steps of an outbreak investigation. (10 points) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Page 9