You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
to estimate the effect of the dioxin crisis on the number of campylobacter infections , a model was designed by which the number of expected cases for 1999 could be calculated .
this model was based on the data collected by the sentinel laboratory surveillance network from 1994 to 1998 .
the cumulative numbers per week were used to drive a monthly chronologic series for 1994 to 1998 and modeled according to the fourier transformation ( 18,19 ) .
this procedure explains the cyclic patterns of data by spectral analysis ; a complex time series with cyclic components is decomposed into sine and cosine terms describing the seasonal changes and a linear term to identify the trend ( figure 1 ) .
the final model has three cyclical terms ( 52 , 26 , and 13 weeks ) , i.e. , a strong yearly variation and two harmonics at the half and quarter year .
the linear trend shows a yearly increase from 1994 to 1998 , with a slope of 15% . when the cyclical contributions are included , r=0,86 , that is , 86% of the variation in the number of the campylobacter infections can be explained by the model .
the epidemic threshold is set at a distance of 1.96 standard deviations ( sd)(95% confidence interval [ ci ] ) , which has shown to be useful for distinguishing epidemic increases from random variation ( 18 ) , or ( as for the dioxin crisis ) exceptional , epidemic decrease .
figure 2 shows the model , including the 95% ci and the actual numbers by which it was calculated .
poultry production per workday for 1998 and 1999 is also shown , representing the production per workday in indices with 1995 as reference year ( 1995 = 100 ) ( 20 ) .
campylobacteriosis in belgium at period of dioxin crisis , model 1994 - 1998 and poultry production index .
age and gender distribution during the crisis was compared with the monthly distribution of age and gender in previous years .
the model was made with ms excel 2000 ; spss version 9.0 was used to compare distributions .
figure 2 shows the model , including the 95% ci as calculated from the numbers in the previous years during a period of 20 weeks ( middle of april to the end of august , weeks 15 to 35 ) as well as the actual count for this period in 1999 .
the number of campylobacter infections analyzed by the sentinel laboratory surveillance network fit the 95% ci except during the dioxin crisis ( from week 21 ) , when all poultry and eggs were taken off the supermarket shelves .
the number of campylobacter infections from week 23 to week 26 in 1999 is on average 94 cases per week or almost 40% lower than the expected average of 153 cases per week ( sdmodel=15 cases / week ; sd = standard deviation ) .
overall , for the month of june ( week 23 to 26 ) , the expected number of infections was 643 ( stmodel=61 cases / month ) while the actual number of cases in 1999 was 375 .
the monthly calculated numbers follow the same trend as campylobacter infections in 1999 and a similar decrease in numbers during the dioxin crisis . after 4 weeks , the ban was lifted , and the number of campylobacter infections returned to the interval calculated by the model .
poultry production , even though over a longer period , also returned to levels comparable with the month of the previous year ( 1998 ) .
there was no difference in age or gender distribution of campylobacter infections during the crisis compared with the rest of the year .
the economic impact is probably the easiest to determine , as this aspect is data driven .
however , the dioxin crisis had a tremendous impact on health and health - related matters , including food consumption .
the sudden change in food consumption , related to the withdrawal of poultry and eggs , had an immediate effect on the number of foodborne diseases , e.g. , campylobacter .
the fitted model shows an unexpected decline in june 1999 . even though the decline in numbers is not exceptional ,
looking at other declines in the number of campylobacter infections , as in february 1996 or february 1997 , these happen during a downward trend in numbers , while the drop in june 1999 occurs when numbers would normally be increasing .
the decline in campylobacteriosis and the lack of poultry in shops lasted 4 weeks , exactly the period from seizing all belgian chicken and egg products from the supermarket shelves until the return of these items .
this supports a direct link and contradicts a possible  ecological fallacy  as the time frame , which has an abrupt beginning and end , is similar for both the dioxin crisis and the decline in number of campylobacter infections ( 21 ) . during this period
a major concern with ecologic studies is often the flue line ( generally , the geographic boundaries of the occurrence of the risk factor and the occurrence of the illness ) , as was the case in the european study of the association between olive oil and cancer ( 22 ) .
the dioxin crisis differs from the commonly analyzed ecologic studies in this geographic aspect , since the borders of the impact of the dioxin crisis are the same as the borders of a well - established surveillance system .
campylobacter is associated with several risk factors and risk behaviors , such as contact with farm and domesticated animals ( mainly cats and kittens ) ( 1012 ) or recent history of antibiotic use ( 14 ) .
however , the dioxin crisis would not have an immediate effect on these factors , as it was primarily a food scare .
drinking raw milk , occasionally found to be a risk factor ( 12,16 ) , is also unlikely to have a contributed to the decline in numbers since milk products were not taken off the shelves .
meat , in particular pork prepared on the barbecue , is generally accepted to be an important risk factor ( 10,16 ) .
pork meat is associated with c. coli , which accounted for 12% ( in 1998 ) and 21% ( in 1999 ) of all campylobacter infections ( 4 ) .
meat remained available during the crisis , which might explain the small increase in c. 
 coli infections , as it is imaginable that chicken , which is the main source of c. jejuni infections , was replaced by pork during the crisis .
eggs were not on sale during the crisis , but they are generally not associated with campylobacter contamination .
the withdrawal of chicken and all related products from the supermarket during the dioxin crisis is the most likely reason for the sudden decline in campylobacter infections .
chicken is found to be the principal source of infection in most case - control studies ( 11,13,14,16 ) . in seattle ,
rare , raw , and cooked chicken were all significantly associated with campylobacter infection ( 8) . undercooked chicken was found to be a risk factor in a colorado study ( 12 ) .
handling raw and even frozen chicken , possibly because of cross - contamination in the kitchen , has also been significantly associated with campylobacteriosis ( 10 ) .
as all belgian poultry was withdrawn , our data allow an estimation of the number of campylobacter infections directly related to poultry .
the decline in the number of campylobacter infections in belgium by 40% was due to the withdrawal of belgian poultry from the market . in 1999 , 199,251 tons of poultry meat was available for human consumption ; 81,261 tons ( 41% ) was imported ( 23 ) .
foreign poultry remained available on the market . according to a marketing bureau that investigates trends in shopping behavior of 3,000 families in belgium ,
eating habits have changed little because of the dioxin crisis ( 24 ) ; moreover , the overall purchase of poultry in 1999 increased by almost 9% .
however , a shift was seen in the quality of the poultry sold ; after the crisis , consumers preferred chicken with some sort of quality label , even though the current labels do not specifically address contamination issues .
besides the 40% decrease in campylobacter infections during the dioxin crisis , this experiment also highlights the remaining baseline of 60% , averaging 75 infections a month . according to an analysis of foodborne disease information in the united states ( 1999 ) , only 80% of the campylobacter spp .
furthermore , as only belgian chicken was banned and non - belgian poultry was still on sale , a number of poultry - related infections are still present in the reported numbers . with at least 40% of the campylobacter infections in belgium explained by poultry and 20% by non - foodborne causes , the source of the remaining infections should be further explored and investigated . the use of a disaster as an epidemiologic tool offers a unique opportunity to observe exceptional changes in the occurrence of infections or other diseases .
the causes or consequences of the crisis can serve as treatment in an uncontrolled natural experiment .
the dioxin crisis as experiment showed that > 40% of the campylobacter infections can be attributed to poultry .
in june 1999 , the dioxin crisis , caused by dioxin - contaminated feed components , exploded in belgium , resulting in withdrawal of chicken and eggs from the market . through the sentinel surveillance system , a decrease in campylobacter infections during june 1999 was noticed . 
 a model was generated with the reports from preceding years ( 1994 to 1998 ) , and a prediction of the number of infections in 1999 was calculated . 
 the model shows a significant decline ( 40% ) in the number of infections , mainly because of the withdrawal of poultry . the use of a disaster as an epidemiologic tool offers a unique opportunity to observe exceptional changes in the occurrence of infections or other diseases .