Pseudonomas Folliculitis or Hot Tub Folliculitis was suffered by the clinic patient in the Season 5 episode "Saviours". It is commonly found in hot tubs, water slides etc.
From Wikipediea "This condition is caused by an infection of hair follicles due to the bacteria Pseudomonas aeruginosa. The bacteria is commonly found in hot tubs,water slides, and such places. Children are more prone to this because they usually stay in the water longer than adults. Hot tub folliculitis appears on the skin in the form of a rash, roughly resembling chicken pox and then developing further to appear as a pimple. Hot tub follicultis can be extremely painful and/or itchy, and left alone without scratching will go away much more quickly. If the rash is aggravated, it can stay, worsen, and spread lasting for months. By that point it is much more difficult to treat. The dots usually go away after about 7 to 10 days, but the condition leaves a hyperpigmented lesion that goes away after a few months.Normally, the rash does not need specific treatment and will go away on its own. Antibiotics may be prescribed in some cases. If the rash continues to appear longer than the 7 to 10 day time period, a physician should be consulted. Folliculitis that is not treated properly could worsen and cause abscesses."