Hospital-acquired Legionella pneumonia has a fatality rate of 28%, and the principal source of infection in such cases is the drinking-water distribution system. Epidemiology
Legionnaires disease acquired its name in July 1976, when an outbreak of pneumonia occurred among people attending a convention of the American Legion at the Bellevue-Stratford Hotel in Philadelphia. Of the 182 reported cases, mostly men, 29 died. On 18 January 1977, the causative agent was identified as a previously unknown strain of bacteria, subsequently named Legionella, and the species that caused the outbreak was named Legionella pneumophila. Following this discovery, unexplained outbreaks of severe respiratory disease from the 1950s were retrospectively attributed to Legionella. Legionnaires disease also became a prominent historical example of an emerging infectious disease.Outbreaks of Legionnaires disease receive significant media attention, but this disease usually occurs in single, isolated cases not associated with any recognized outbreak. When outbreaks do occur, they are usually in the summer and early autumn, though cases may occur at any time of year. Most infections occur in those who are middle-aged or older. National surveillance systems and research studies were established early, and in recent years, improved ascertainment and changes in clinical methods of diagnosis have contributed to an upsurge in reported cases in many countries. Environmental studies continue to identify novel sources of infection, leading to regular revisions of guidelines and regulations.
Duodenal lymphocytosis, sometimes called lymphocytic duodenitis, lymphocytic duodenosis, or duodenal intraepithelial lymphocytosis, is a condition where an increased number of intra-epithelial lymphocytes is seen in biopsies of the duodenal mucosa when these are examined microscopically. This form of lymphocytosis is often a feature of coeliac disease but may be found in other disorders. Presentation
The condition is characterised by an increased proportion of lymphocytes in the epithelium of the duodenum, usually when this is greater than 20-25 per 100 enterocytes. Intra-epithelial lymphocyte (IEL) are normally present in intestine and numbers are normally greater in the crypts and in the jejunum; these are distinct from those found in the lamina propria of the intestinal mucosa. IELs are mostly T cells. Increased numbers of IELs are reported in around 3% of in duodenal biopsies, depending on case mix, but may be increasingly being found, in up to 7%. Causes
The list of possible causes is wide, including coeliac disease, environmental enteropathy (tropical sprue), autoimmune enteropathy, small intestinal bacterial overgrowth, NSAID damage, Helicobacter pylori, other infections and Crohns disease. Diagnosis
Diagnosis is made by accurate counting of intraepithelial lymphocytes during histological examination of the duodenum. The definition of the condition includes the requirement that the duodenal histological appearances are otherwise unremarkable, specifically with normal villous architecture.In coeliac disease (also known as gluten-sensitive enteropathy), duodenal lymphocytosis is found in untreated or partially treated cases. This is the least severe type of change, known as the Marsh I stage, in the classification of histological changes in coeliac disease.