You think your job is tough? Some scientists examined sewage from Pittsburgh, Barcelona and Addis Ababa in a hunt for unknown viruses.
They found scads. How many? At least 43,381.
To put that number into perspective, consider that up to now scientists have charted only about 3,000 viruses. And among the known viruses found in the sewage samples, only 17 were bugs that cause human disease — things like the common cold virus, diarrhea-causing Norwalk virus and human papilloma virus, or HPV, which causes cervical cancer and genital warts.