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MERS is rare in adults, especially elderly people. We herein report a man in his 60s diagnosed with MERS caused by <jats:italic>Legionella<\/jats:italic> pneumonia. He completely recovered with only the administration of levofloxacin and azithromycin despite the risk factors of an advanced age, medical history of untreated hypertension, bilateral spontaneous pneumothoraxes, smoking and drinking habits and pulmonary emphysema. To our knowledge, this is the oldest case of MERS due to <jats:italic>Legionella<\/jats:italic> pneumonia and extremely old among total MERS cases. Our research revealed that <jats:italic>Legionella<\/jats:italic> species are the most common pathogens of adult-onset MERS, while viruses are the main causative factors in children. This case helps clarify the features of MERS in high-risk adults.<\/jats:p>","DOI":"10.1136\/bcr-2022-252994","type":"journal-article","created":{"date-parts":[[2022,12,30]],"date-time":"2022-12-30T09:45:45Z","timestamp":1672393545000},"page":"e252994","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":2,"title":["Case of clinically mild encephalitis\/encephalopathy with a reversible splenial lesion (MERS) due to <i>Legionella<\/i> pneumonia"],"prefix":"10.1136","volume":"15","author":[{"given":"Satoko","family":"Kageyama","sequence":"first","affiliation":[{"name":"Internal Medicine, Kosei General Hospital, Mihara, Hiroshima, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ruiko","family":"Hayashi","sequence":"additional","affiliation":[{"name":"Internal Medicine, Kosei General Hospital, Mihara, Hiroshima, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Haruhito A","family":"Uchida","sequence":"additional","affiliation":[{"name":"Nephrology, Rheumatology, Endocrinology and Metabolism, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan"},{"name":"Chronic Kidney Disease and Cardiovascular Disease, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2022,12,30]]},"reference":[{"key":"2025082800503064000_15.12.e252994.1","doi-asserted-by":"publisher","DOI":"10.1016\/j.braindev.2009.02.012"},{"key":"2025082800503064000_15.12.e252994.2","doi-asserted-by":"publisher","DOI":"10.1212\/01.WNL.0000144274.12174.CB"},{"key":"2025082800503064000_15.12.e252994.3","doi-asserted-by":"crossref","DOI":"10.1097\/MD.0000000000017982","article-title":"Mild encephalitis\/encephalopathy with a reversible splenial lesion secondary to encephalitis complicated by hyponatremia: a 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