Attack Rate in Food Poisoning: Order in Chaos

The frequency distributions of the numbers of patients and eaters were near lognormal for almost all food poisonings. The medians and ranges remained almost unchanged over time, although the annual number of incidents varied. However, the numbers of patients and eaters were not correlated for many of the food poisonings. A regular pattern relating the numbers of patients and eaters emerged for food poisonings exhibited strong seasonal incidence. For example, food poisonings caused by norovirus or Campylobacter spp. exhibited a comb teeth-like pattern in the plot comparing the ranking numbers of patients and that of eaters, and fingerprint-like pattern in the plots comparing the attack rate and number of patients or eaters. Meanwhile, food poisonings with low incidence and without seasonality, such as those caused by Clostridium perfringens, exhibited amorphous patterns in both plots. Further analysis indicated the occurrence of these patterns was determined by the combination of pathogens and services, and not by either factor alone. Thus, the emergence of a regular pattern may be associated with "complexity" nature of food poisoning.