Questions about the 2011 E. coli Outbreak in Germany

It appears that the Escherichia coli (abbreviated as E. coli) O104:H4 strain in Germany was spread mostly by contaminated sprouts, and in just a few cases, from close contact with a sick person. E. coli are a large and diverse group of bacteria, and not all strains of E. coli bacteria are harmful. However, E. coli O104:H4 has several genetic factors that contribute to its ability to cause sickness. These factors are already well known to scientists and occur in various strains of E. coli in nature. There is no reason to think that this strain was modified intentionally.  Because of minimal person-to-person spread of this strain, there is also no reason to think it will cause a pandemic. 

E. coli O104:H4, can make a potent Shiga toxin, as can most strains in the serotype O157:H7, and some other E. coli strains. This toxin is dangerous as it can attack the body in several areas: the gut (causing bloody diarrhea), the kidneys (causing kidney failure), and sometimes the nervous system.  The toxin can cause clots to form in small blood vessels. As red blood cells try to pass through the clots they get damaged (causing anemia). To make matters worse, this E. coli O104:H4 strain also has some genes that are found in another group of E. coli called enteroaggregative E. coli. On its own, diarrhea from enteroaggregative E. coli is not usually serious, but combined with Shiga toxin it can make people very sick. More research on enteroaggregative E. coli needs to be done, but so far, what we do know comes from studies of humans with diarrhea. Little work has been done to look for it in animals or in the environment. It is possible that there are animal reservoirs of enteroaggregative E. coli, and scientists haven’t discovered them yet.

The combination of Shiga toxin and enteroaggregative features has been seen before;  1) in E. coli O104 identified in Europe and Asia in the last decade, and 2) in a different strain of E. coli that caused a small outbreak in Europe in the 1990s.  While this combination is uncommon, it is not new.

The strain of E. coli O104:H4 causing the outbreak is resistant to many antibiotics, because it has many genes that code for that resistance. Since CDC doesn’t recommend that STEC infections be treated with antibiotics, the fact that this strain is antibiotic resistant is not likely to impact the care that sick people receive. The presence of these genes simply means that the bacteria were likely, at some point in the past, to have been in environment with antibiotics in it.  Other bacteria occur with this level of resistance.  There is no reason to think that this strain has been modified intentionally to be antibiotic resistant.

The outbreak in Germany underscores the critical importance of all aspects of public health, including the following: continuous public health surveillance to detect disease outbreaks; rapid epidemiological investigation of outbreaks; public health reference laboratories that can examine and identify uncommon organisms that sometimes cause disease; and food safety authorities that take appropriate measures to control the source of the infection and to prevent similar events from happening in the future.