Infectious diseases cause one-third of all human deaths worldwide. Microbiologists are beginning to get a clearer picture of some of the bacteria that cause disease, using the increasing number of genome (gene) sequences available for these microbes. In fact, a back log of genetic data is waiting to be prioritized and analyzed. The data shows transfer of genetic material between bacteria seems to be much more common than previously believed. Essentially, bacteria can exchange genes that cause disease. In addition, a significant portion of the genes associated with disease are found in clusters called “pathogenicity islands.” William Hsiao believes that focusing on these genomic islands will narrow the search for disease-causing genes in bacteria. He hopes the information will explain how some bacteria cause disease and how they differ from bacteria that do not.