Triathletes racing in Ironman distance events are prone to a number of injuries and illnesses. There have been a number of studies done evaluating medical problems that develop during a triathlon. As one might imagine, the longer the triathlon the greater the percentage of racers seeking medical assistance. In an Olympic distance race usually fewer than 2% require aid. For a 1/2 Ironman the number is 10%, and for a full Ironman it is about 20%. These numbers represent only the athletes who seek aid on race day. No-one knows how many get sick in the days following the event. The most common reasons for seeking aid during an Ironman are dehydration, heat illness, and hyponatremia (low serum sodium). Most of these problems become apparent during the run or just after crossing the finish line.
I don't have any data from the medical personnel at Canada, but I imagine that their records indicate the expected frequency and type of illness/injury seen in other Ironman events. At this point, I don't think it was the water or Endura or any other common factor, other than it was an Ironman race. (But I am interested in hearing more if any one has any additional information.) These races are incredibly taxing on the body. The repair process takes weeks and it is not over when the soreness disappears.
After a race you are transiently immunosuppressed and are thus susceptible to a whole variety of infections -- especially viruses. Combine this fact with the great number of people from all over the world gathered together and it is no wonder the risk of infection is much greater.
With respect to illness during a race, I'll briefly hit on the topic of hyponatremia. There have been a few medical studies done during the Ironman in Hawaii and hyponatremia is very common. Random blood sample were taken from athletes seeking aid and from those who did not. 25% of the "healthy" athletes had a low serum sodium following completion of the race, whereas 60% of those in the medical tent had a low sodium. A low serum sodium can cause several symptoms -- nausea, fatigue, vomiting, lethargy, weakness, somnolence, seizures, coma, and death. The lower the sodium, the more severe the symptoms. The reason hyponatremia is so common during an Ironman and is rare in Olympic distance events, is related to the length of the event. Sweat in athletes in approximately 1/4 Normal Saline (1/4 the concentration in the blood) which is a 0.225% salt solution (blood is 0.9%). The average sweat rates during the event are about 1 - 1.5 liters per hour. Thus for a finishing time of 13 hours one might lose 26 - 39 grams of NaCl. Most of the fluid replacements used and the foods eaten are relatively low in salt. Thus replacing lost water without replacing sodium causes hyponatremia. Few of the commercially available sports drinks contain sufficient sodium to replace losses that occur during an Ironman. You must eat or supplement your intake of NaCl. For races lasting longer than 4 hours, some medical authorities have recommended consuming foods or liquids containing salt such that 1-2 grams of sodium per hour are ingested. Note:2.5 grams of table salt consists of approximately 1 gram of sodium and 1.5 grams of chloride.