Leptospirosis is a bacterial infection that occurs throughout the world but particularly in tropical area and does exist in Hawaii. It may be contracted in fresh water streams. The contagion in most cases is urine or feces from animals that may have infected the waters upstream. These animals can often be rats, mice, mongoose, feral pigs, cattle, or various other forms of livestock.
Symptoms of an infection are generally flu like and can range from moderate to severe.
With regard to avoiding infection in Hawaii streams and fresh water areas be sure not to go in the water if you have open abrasions or cuts and since the other main way to catch the disease is by drinking the water or having it enter through the eyes or nose the best preventative measure would be to swim with your head above the water.
Although the disease is fairly rare it does appear in Hawaii about 50-100 times each year. If you feel that you may have been infected see a doctor as soon as possible. The Disease Outbreak Control Division dealing with Leptospirosis is found on Oahu and their number is 808-586-4586.