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1 Disease Detectives Divisio C Natioal Sciece Olympiad May 25 i their li fetime. The survey also asked "Durig the past 12 moths, have you had a episode of asthma or a asthma attack?" Agai, iformatio o childre was collected from adult proxies. This evet icludes two problems. Problem! is a tie breaker. Problem : Disease Detectives Attack the Public Health Problem of Total Suggested time = 3 miutes Table 1 shows the results from NHS surveys from 198 through (3 pts) Usig the above iformatio, geerate a case defiitio for asthma. Aswer (3 poits[ay/}): is a chroic disease that affects the lugs, causig repeated episodes of wheezig, breathlessess, chest tightess, ad ighttime or early morig coughig. These episodes, or "asthma attacks" as they are ofte ca lled, occur whe the sides of the airways i the lugs become iflamed ad swolle. Muscles aroud the airways tighte, ad less air passes i ad out of the lugs. Excess mucus forms i the airways ad clogs them eve more. 2 1, 2.3 millio Americas had asthma, ad 12 millio had had a asthma attack i the previous year. More tha 5, Americas died from asthma each year from 1993 through The cost of asthma i the Uited States i 2 was estimated to be aroud 13.8 billio dollars. Although family history cotributes to susceptibility to asthma, the cause is ukow i most cases. Evirometal "triggers," such as cockroaches, dust mites, furry pets, mold, tobacco smoke, ad certai chemicals are thought to trigger asthma attacks amog sesitive idividuals. A case of asthma ca be defied as: a perso who has experieced repeated episodes of wheezig, breathlessess, chest tightess, ad ighttime or early morig coughig, OR a perso who has bee diagosed by a physicia as havig asthma. Table 1. Prevalece* of self-reported asthma ( ) ad of a episode of asthma or asthma attack ( ) durig the precedig 12 moths, by race, sex ad age group. Self- reported asthma prevalece durig the precedig 12 moths White Black Other r-- Havig asthma does't.-(' _,,rl stop me or my frieds! Episode of asthma or asthma attack durig the precedig 12 moths Race l!jfj,..;i Sex \ Male Female l.j -.l ll j ' )! l " JllJ.\ (".«ii Age group (yrs). ''' - J! \!f19,m Figure : Drawig by Jasmie Ferrell, Ti lso Elemetary School, Atlata GA. Wier of 22 CDC Wor ld Day Poster Competitio Disease detectives have obtaied mu ch of their iformatio o the occurrece of asthma ad asthma attacks i the Uited States from the Natioa l Health terview Survey (NHS), which is based o a probabi lity sample of the coutry's civilia, oistitutioalized populatio (e.g., those ot i log term care or icarcerated). Before 1997, the NHS collected data o asthma from oe-sixth of the sampled household s. A kowledgeable adult family member, usually a paret, respoded as proxy for childre. People who aswered, "Yes," to the questio, "Durig the past 12 mo ths, have you had asthma?" were couted as havi g the co ditio. 1997, the NHS bega collectig iformatio o astt,,a from a radomly selected child ad a radomly selected adu lt i every househo ld. Those who aswered, "Yes," to the questio, "Has a doctor or othe r hea lth care professioa l ever told yo u that yo u had asthma?" were couted as havig had asthma '.:' Total Source: Maio OM et al., Surveillace for asthma-uited States, MMWR 22;5l(SSO):1-13 *Estimated; per 1, populatio. 2. (2pts) Defie prevalece. A11swer (2 poits [ay!}): PREVALENCE: The umber of cases of a give disease or other attribute that exists i a defied populatio at a specified time; OR PREVALENCE RA TE: The proportio of the populatio with a disease or other attribute i a defied popul atio at a specified time. Total Poits this Page 3

2 childre aged 18 years i their aalysis. Parets aswered for their childre regardig the presece of childhood asthma. Family icome was expressed as a ratio of actual family icome ad the icome threshold for the Federal Poverty Level (FPL). The FPL is a dollar amout below which a family or household is cosidered to be i poverty. Table 2, o the ext page, shows some of the results of this aalysis. Table 2. Characteristics of sample childre, as reported by adult proxies, ad asthma prevalece by demographic cateory." (Both aswers are acceptable because the word "prevalece" is sometimes used iterchageably with "prevalece rate" ad was probably what should have bee asked i this questio.) 3. Refer to the data i Table!. a. (2pts) Explai the differece betwee the estimated prevalece of asthma before 1997 ad the umber of people rep1tig a episode of asthma or a asthma attack durig the precedig 12 moths durig 1997 ad later. These are two differet measures. Betwee 198 ad 1996, the survey described the respodets' report of havig asthma durig the previous 12 moths - the self-reported asthma prevalece durig the precedig 12 moths. After 1997, the survey described episodes of asthma or asthma attack amog the respodets durig the precedig 12 moths, ot the prevalece. So, prior to 1997, this table shows asthma prevalece; durig ad after 1997, it shows attacks. b. (3 pts) Accordig to the 1999 NHS data provided i table, which groups have the greatest prevalece of asthma? Total sample (N=l4,244) Lifetime asthma prevalece Weighted percet Weighted percet No-Hispaic white 65.2 i 1.2 Demographics Child race/ethicity.3 No-Hispaic black Hispaic l Other The groups with the greatest asthma prevalece caot be ascertaied. Sice may with asthma have their symptoms uder cotrol, there may be some who have asthma but do't have attacks. 1999, the table shows oly attacks, ot how may had asthma i the precedig 12 moths Aswer (3 poits [ay ]): -3 (") 9" rj'j.. 1 Male Female Family icome-to-fpl ratio. The groups with the greatest (apparet) asthma prevalece are: o Blacks o Females o 5-14 year olds, OR Although blacks, females, ad 5-14 year olds appear to have higher prevalece, it is ot possible to ascertai which groups have the greatest prevalece without kowig the results of sigificace tests FPL : 2 FPL Referece group i- Discuss: would't be able to say which group is higher i race or age because the sigificace test is based o all the categories of race ad all the categories of age. However, the origial table has Aswer (3 poits, poit per correct relatioship): foototes for race that idicate Geder: Males have a higher prevalece of lifetime asthma sigificace but the foototes are tha females ot reproduced i this table. Accept Race/ethicity: No-Hispaic blacks have a higher prevalece as a correct aswer that there is a of lifetime asthma tha those of other races/ethicities associatio betwee race ad Age: Childre have a higher prevalece of lifetime prevalece of asthma ad betwee asthma tha childre i other age groups age ad asthma? 4. Refer to the data i Table 2. a. (3 pts) Which groups have the highest prevalece of lifetime asthma? Aswer (6 poits, 2 poits per explaatio): There may be a geetic compoet ad blacks may be more likely to develop asthma tha other groups There may be a evirometal compoet ad blacks may be more likely to be exposed to triggerig agets tha other groups There may be a reportig bias ad other people may be less likely to be diagosed with asthma tha blacks. Usig data from the 1997 NHS, disease detectives examied the associatio betwee race/ethicity ad family icome ad the prevalece of lifetime childhood asthma. They used cross-sectioal data o 14,244 Total Poits this Page.5 FPL FPL 'Smith LA, Hatcher-Ross JL, Wertheimer R, Kah RS. Rethikig race/ethicity, icome, ad childhood asthma: racial/ethic disparities cocetrated amog the very poor. Pblc Hlth Rpts 25; 12: d. (6 pts) Propose three possible explaatios for the apparet lik betwee race/ethicity ad asthma? """""' rj'j. t.rj 7.8 Child geder c. (3 pts) Accordig to the 1996 data, which groups have the greatest prevalece of asthma?.1 Child age (years) Aswer (3 poits): p-value 4 Note: A aswer that says "No-Hispaic black, male childre have a higher prevalece of lifetime asthma" would be icorrect because this is ot a multivariate aalysis. 5 tf'j r: z.._,

3 b. (2 pts) How is the prevalece oflifetime asthma related to family icome? Aswer (2 poits [ay!]): prevalece did ot vary sigificatly by icome-to-fpl-ratio; the other groups are ot sigificatly differet from the referece group; OR There is a suggestio of a relatioship betwee asthma prevalece ad family icome, but it is ot statistically sigificat. There is o statistically sigificat differece betwee Hispaics ad o-hispaic whites i the lifetime prevalece of asthma. the secod poverty level, Hispaic ethicity may be protective. 8. (6 pts) Disease detectives sometimes use race ad ethicity as a surrogate for socioecoomic status. Race ad ethicity are geerally self-reported variables ad askig people about their race or ethicity is cosidered a less sesitive issue tha askig about their icome or educatioal level. Give two reasos that self-reported race or ethicity may ot be a valid idicator of social ecoomic status. Aswer (6 poits, 3 per reaso [ay 2}): The associatio betwee race/ethicity ad SES is ot perfect. Racial groups are ot homogeeous with respect to culture or SES. There are o categories for people of mixed racial/ethic backgrouds which forces them ito artificial groups. People may chage their reported race/ethicity depedig o circumstaces. Disease detectives coducted a stratified aalysis, comparig the prevalece of lifetime asthma amog racial/ethic groups for the various levels of family icome-to-fpl ratios ad expressig the results as odds ratios (ORs) after adjustmet for a umber of sociodemographic variables. Results are show i Table 3. Table 3. Associatio of race/ethicity with lifetime asthma prevalece, by icome-to-fpl ratio FPL FPL 2FPL No-Hispaic black 1.99 (1.9, 3.64) 1.9 (.7,1.7) 1.23 (.89, 1.71) 1. (.78, 1.28) Hispaic.96 (.51, 1.79).64 (.4,.99) 1.2 (.73, 1.43).91(.71,1.16) No-Hispaic white Referece Referece Referece Referece Smith LA, Hatcher-Ross JL, Wertheimer R, Kah RS. Rethikig race/ethicity, icome, ad childhood asthma: racial/ethic disparities cocetrated amog the very poor. Pblc Hlth Rpts 25; 12: (2 pts) Explai how the data from No-Hispaic whites was used i these aalyses? Aswer (2 poits, per elemet): ;:5 \ Large scale reductios i air pollutio are difficult to implemet ad to study over a short period of time. 1996, however, the teratioal Olympic Games held i Atlata offered a excellet opportuity for this type of study. Adjusted ORs (95% Cl).5 FPL ****** The No-Hispaic white group was used as a referece or compariso group because each of the other two groups was compared to the No-Hispaic whites. The evet brought more tha millio visitors to the city. To reduce traffic, busiesses ad state ad local gc1vemmets authorized a umber of chages ad programs. These icluded icreasig public trasportatio, approvig alterative work hours ad telecommutig, ad restrictig traffic. Most of the veues were accessible by public trasportatio, ad may residets took time from work to atted the games. Others left tow or stayed home to avoid the crowds. Disease detectives suspected that these chages may have improved air quality eough to reduce asthma attacks amog.:hildre i the area. Usig a ecologic study desig, ivestigators compared a umber of variables durig the 17 days of the games with those durig 4-week periods before ad after the games. The primary variables studied were the umber of citywide hospitalizatios, acute care visits, ad urget care ceter visits for asthma ad o-asthma coditios amog childre 1 to 16 years of age i the fi ve cetral couties of metropolita Atlata. O Table 3 was a multivariate aalysis ad cotrolled for a umber of factors (asthma, icome-to-fpl ratio, race/ethicity). Table 2 was a bivariate aalysis ad oly looked at two variables at a time, oe of which was asthma.,-...._. a. (2 pts) What is the group used as the uit of aalysis i this study? A11Swer (4 poits, 2 per limitatio [ay 2}): Total Poits this Page tfj z b. (4 pts) Describe two limitatios to ecologic studies i compariso with case-cotrol, cohort, or prospective studies. 6 Childre 1-16 years of age i the 5 cetral couties of metropolita Atlata are used as the uit of aalysis. Oly i the.5 icome-to-fpl ratio was the prevalece of asthma for o-hispaic black childre higher tha the prevalece for o-hispaic white childre whe cotrollig for sociodemographic variables. Except for the very lowest ratios oficomt::-to-fpl (the poorest group), there is o statistically sigificat differece betwee o-hispaic blacks ad o-hispaic whites i the lifetime prevalece of asthma. 9. ecologic studies, groups, rather tha idividuals, are used as the uit of aalysis. Because groups are usually defied i tes of geographic areas i which mortality or icidece data are available, ecologic studies ca make use of existig data ad be coducted quickly ad iexpesively. 7. (6 pts) What two coclusios do you draw from the results i Table 3 about the relatioships betwee race/ethicity ad fami ly icome ad childhood asthma? Aswer (6 poits, 3 per coclusio [ay 2}):. Data were obtaied from a variety of sources icludig Georgia's Medicaid claims fi le, the patiet database of a health maiteace orgaizatio, computerized emergecy departmet records from two of Atlata's three pediatric hospitals, ad the Georgia Hospital Discharge Database. 6. (4 pts) How does Table 3 differ from Table 2? Aswer (4 poits): w. 7

4 -1 1. Ecologic studies look at group level effects while the other desigs look at idividual level effects, so it is ot possible to evaluate the relatioship betwee idividual exposures ad risks. Thus, there is a possibility of makig a ecological fallacy (a ecological fallacy is a error of reasoig that ca occur because group differeces may be the result of somethig urelated to the exposure). Data o exposure ad outcome geerally come from secodary sources that have bee collected for other purposes, meaig that the data is sometimes ot ideal for testig a give hypothesis. Usig summary measures for exposure or outcome may lead to imprecise or ustable associatios if a high degree of variability exists withi the ecological uits beig studied. ecologic studies it is difficult to cotrol for potetial cofouders because data o potetial co fouders is ofte uavailable or of icosistet quality. t may be impossible to establish a correct temporal sequece betwee exposure ad outcome due to limited data. (6 pts) Give three examples of pediatric asthma evets that might ot be foud i the above datasets. Weekday morig rush hour traffic couts decreased 22.5%. Weekday total 24-hour traffic rates decreased 2.8%. Weeked morig rush hour traffic rates decreased 9.7%. Use of public trasportatio icreased 217%. Table 4. Relatioship betwee acute asthma evets ad the 3-day cumulative ozoe levels durig the 73day summer stujy period.* Data Source Ozoe 6 ppb Mea Ozoe 6-89 ppb Mea (95% C) Ozoe::;: 9 ppb Mea (95% C) Georgia Medicaid Claims l.61 ( ) ( ) Health Maiteace Org l.33 ( ) ( ) Aswer (6 poits, 2 poits per example [ay 3)): that did ot lead to a medical itervetio. that were treated outside of the geographic area. that were treated i the area but i facilities that were ot icluded i the databases. that took place amog childre already i the hospital for aother reaso. (5 \ compariso with the baselie period, the umber of asthma emergecy care visits ad hospitalizatios durig the Olympics decreased 4 l.6%. The umber of asthma-related emergecy departmet, urget care visits, ad hospitalizatios amog HMO erollees decreased 44.1 %. -related visits to two large pediatric emergecy departmets decreased. %. Citywide hospitalizatios for asthma decreased 19.1 %. These equate to 3, 1, 9, ad 7 fewer emergecy asthma evets, respectively, tha would have bee expec.ted o the baselie averages. 11. a. (1 pt) Ca you use these data to determie the total differece i umber of emergecy asthma attacks durig the games ad durig the baselie? Aswer { poit): No. b. (2 pts) f so, what is the differece? f ot, why ot? dividuals' asthma attacks may be represeted i more tha oe datasets, so addig the umbers would result i duplicate couts because the same idividual/attack/evet might be couted more tha oce. vestigators obtaied iformatio o air quality from the U.S. Evirometal Protectio Agecy ad the Georgia Departmet of Natural Resources. They obtaied hourly traffic data from four Georgia Departmet of Trasportatio moitorig sites. A time series regressio model was used to cotrol for weather variables, serial correlatio, ad day of the week. Aalysis idicated that levels of Ozoe decreased 13% (p =.6) Carbo mooxide decreased 18.5% (p =.2) Particulate matter decreased 16.1 % (p =.1) Nitroge dioxide decreased 6.8% (p =.49) Sulfur dioxide icreased 22.1 % (p =.65) 8 Pediatric Emergecy Depts ( ) ( ) Georgia Hospital Discharge ( ) ( ) 7'J). * Friedma MS et al. mpact of chages i trasportatio ad commutig behaviors durig the 1996 Summer Olympic Games i Atlata o air quality ad childhood asthma..tama 21 ;285(7): a. (2 pts) What term do disease detectives use to describe the relatioship betwee the icrease i t-3 relative risk of asthma attacks ad the icrease i cocetratios of ozoe? t-3 Dose respose. b. (2 pts) How does this icrease support the idea of a causal relatioship betwee ozoe levels ad asthma attacks? The demostratio of a dose respose relatioship supports a causal relatioship betwee a evet ad a outcome o a idividual-level aalysis. Sice this was a aggregate aalysis a causal relatioships caot be idicated: it is ot possible to ascertai whether the idividuals havig the asthma attack were the oes exposed to the highest ozoe level or whether the ozoe level icreased before the attack rather tha after it. c. (6 pts) What criteria eed to be demostrated to support a causal relatioship betwee ozoe levels ad asthma attacks? Aswer (6 poits, for each of the criterio [ay 6}): Correct temporal sequece (temporality) Strog associatio Cosistet associatio Dose respose relatioship Biological plausibility Experimetal evidece Specificity of associatio (These are Hill's Postulates or Bradford Hill's Postulates) 9,,-... (1 zt-3.._.

5 , Problem (Tie Breaker): Sick at Sea-Disease Detectives vestigate Acute Gastroeteritis Outbreaks o Cruise Ships recommedatios durig the 6-hour iterval betwee cruses. List two reasoable hypotheses that may explai why the secod group of passegers had so may cases of AGE. Recommeded time: 2 miutes (32 Poits Possible) Backgroud Cruise ship outbreaks demostrate how quickly ad easily some microbes, particularly viruses, ca be trasmitted from perso to perso i a closed eviromet. The result ca be a very large outbreak i the shipboard populatio. 22, CDC's Vessel Saitatio Program oted a sigificat icrease i acute gastroeteritis (AGE) of viral origi. The pricipal pathoges were oroviruses (i.e., Norwalk-like viruses or NL V). NL V is a well-documeted aget of AGE that is resposible for more tha 23 millio cases each year. 1. (6 pts) List three coditios or characteristics of the cruise ship eviromet that are likely to cotribute to AGE outbreaks. 2. (6 pts) Give that most AGE outbreaks attributed to oroviruses are water- or foodbome, list three measures that might prevet AGE trasmissio aboard ship. documetig oe of the 22 AGE outbreaks aboard cruise ships, CDC discovered cliical cases of gastroeteritis o a sigle ship that had bee used for two separate, but cosecutive cruises. Figure below shows the time course ad umber of cases of AGE occurrig aboard this cruise ship betwee July 18 ad August 1, 22. rs - '.i::: , 6 " r JO rj1 4. (6 pts) Accordig to data from the case report, did Cruise or Cruse 2 have the highest attack rate amog both passegers ad crew members? You ca assume that oe of the passegers were ill before either cruise bega. (Note: You MUST SHOW YOUR CALCULATONS to receive full credit for your aswer). r zi 21 2s 2a 'l.l 1-3 z,_, A Date ol oset Passeger disembarkatio at 8: 2..; (cruise 1) embarkatio (cruise 2) at 2: p.m. 3. (4 pts) Note that o July 25, passegers from Cruise disembarked ad a ew group of passegers embarked for aother 7-day cruise. The ship was disifected i accordace with CDC Total Poits this Page trj (] er ,-. Pise. 2l rj (5 pts) Assumig all 25 cases of AGE o July 25 were amog the ew group of passegers for Cruise 2, what is the poit prevalece of AGE o that date? C,uiu 2 Crute.& 1 O July 18, cruise ship A, owed by cruise lie A, embarked 1,318 passegers ad 564 crew members for a 7-day cruise from Vacouver to Alaska. O July 19, five passegers reported to the ship's ifirmary with symptoms of AGE. By July 25, a total of 167 passegers ad ie crew members had reported illess. Amog the 176 patiets, the predomiat symptoms were vomitig (76%) ad diarrhea (73%). Five of stool specimes from ill passegers were positive for orovirus by reverse trascriptase polymerase chai reactio (RT-PCR). O July 25, whe passegers disembarked, the ship was disifected i accordace with CDC recommedatios, ad the same day, a ew group of passegers embarked for aother 7-day cruise. Durig the cruise, 189of1,336 passegers ad 3 of571 crew members had AGE with diarrhea (91%) ad vomitig (85%). 5. (5 pts) Referrig to this same data set (arrative case report ad Figure ), determie the icidece rate of AGE amog passegers o Cruise from July 2 to 25. (Note: You MUST SHOW YOUR CALCULATONS to receive full credit for your aswer). FGURE 1. Number of passegers ad crew members reportig to the ship's firmary with symptoms of acute gastroeteritis durig two cosecutive 7-day cruises o cruise ship A, by date of illess oset - Vacouver to Alaska, July 18-August 1, 22 1 The followig arrative describig the AGE outbreaks depicted i Figure appeared i the Morbidity ad Mortality Weekly Report (MMWR, December 13, 22;5 (49); ): 1 11