| typhoid fever as a cause of opportunistic infection: case report. | typhoid fever is a systemic infection caused by the bacterium salmonella enterica subspecies enterica serotype typhi, which is acquired by ingestion of contaminated food and water. each year the disease affects at least 16 million persons world-wide, most of whom reside in the developing countries of southeast asia and africa. in italy the disease is uncommon with a greater number of cases in southern regions than in northern ones. | 2006 | 16504150 |