I would imagine, given the fact that you state you have cleaned everything thoroughly, this is what's referred to as "Krausen" or "Beer Head" and is perfectly normal and is most certainly NOT an indicator of an infection.
As stated on Wiki: Beer head (also head or collar), is the frothy foam on top of beer which is produced by bubbles of gas, typically carbon dioxide, rising to the surface. The elements that produce the head are wort protein, yeast and hop residue. The carbon dioxide that forms the bubbles in the head is produced during fermentation. The carbonation can occur before or after bottling the beer. If the beer continues fermenting in the bottle, then it naturally carbonates and the head is formed upon opening and/or pouring the beer. If the beer is pasteurized or filtered then the beer must be force carbonated using pressurized gas.
The density and longevity of the head will be determined by the type of malt and adjunct from which the beer was fermented. Different mash schedules and cereal sources influence head retention. In general, wheat tends to produce larger and longer-lasting heads than barley.
In other words - don't worry about it! :-)