Platelets are used when you need your blood to form clots. Usually this is because of an injury such as a cut in which you are bleeding. The more platelets you have the more easily your body can form clots to stop bleeding.

When I take too much advil, my platelet count seems to go down much lower than normal. Aspirin also has an effect.

I don't know about bugs that can influence platelet counts, but it is possible.

Actually it isn't really clear what will affect platelet counts, or if there is anything you can do to raise your level. Mine is fairly high and I regularly donate my extra platelets. I suspect my dad has even more than I do because he has a tendency to form blood clots in his legs; the condition is called DVT, deep vein thrombosis. The blood clots then can break away and travel to the heart, lungs, or brain and cause problems there by interrupting circulation.