There have been several instances of apparent human to human spread of the new E coli attacking Europe, including one in the US. Thus, it seems clear that this pathogen has the potential to infect people long after the original food contamination problem has ended. The risk of extended outbreaks likely will depend on many factors including personal hygiene and water sanitation. However, it would appear that even in countries with relatively well developed public health systems, extended transmission of this bacteria is possible [hat-tip, Helblindi].
From Kyiv Post, June 14, 2011
A third case of infection with the E. coli bacterium has been reported in Poland, Polish media have reported.
A case of the deadly E. coli strain O 104, similar to that earlier detected in Germany, was reported in a 68-year-old woman from Gizycko. The woman took care of the two-year-old brother of a seven-year-old boy previously hospitalized in Warsaw after he came down with an E. coli infection.
The older boy may have contracted the disease after the return of his father from Germany.
According to doctors, the condition of the woman is stable, and she could soon be discharged from hospital.
From this report, it would appear that the father was infected while he was in Germany. He infected his 7 year old son. That boy may have infected his two year old brother. The two year old then apparently infected his 68 year old babysitter. More information on the dates of onset of symptoms for each individual in this cluster would be useful to confirm this apparent human to human to human to human chain of transmission.
Determining the ratio of asymptomatic cases to individuals with serious symptoms is difficult without extensive testing of the general population. However, in this small cluster, it would appear that 50% of the infected were either asymptomatic or had mild symptoms (the father and the 2 year old) while 50% of the infected required hospitalisation (the 7 year old boy and the 68 year old babysitter). Further testing of individuals in close contact to patients in human to human clusters may provide an efficient way to determine the relative numbers of asymptomatic and serious cases.