It seems unlikely that there is a significant health issue associated with dishwashing practice. Reported cases of food poisoning rose by a factor of 6 from 1982 to 2001 - 2001 had a million reported cases (according to the Food Standards agency) - during which period one would presume availability of dishwashers/mixer taps/hot water had increased. Of course, difficult to control for the spread of key bacteria: Salmonella, E. Coli, Campylobacter, Listeria & Clostridium.