Seven months after South Korea identified its first case of Middle East respiratory syndrome (MERS), the country is calling the outbreak officially over as of midnight tonight there. The final patient infected with the MERS virus passed away on 25 November—not from MERS but from the malignant lymphoma that had also prevented him from clearing the virus. Strictly following World Health Organization guidelines, Korean authorities waited 28 days—twice as long as the 14-day incubation period for the MERS virus—to declare an official end to the outbreak.

The last patient, a 35-year-old male, was already suffering from lymphoma when he had contact with a MERS patient on 27 May. Falling ill on 6 June, he was hospitalized at the Samsung Medical Center and confirmed positive for MERS on 7 June. He was later transferred to Seoul National University Hospital where he continued to show signs of  the virus until successive tests on 30 September and 1 October were negative. A 2 October Ministry of Health press release noted that 116 days was the longest time that a confirmed MERS patient has ever remained positive. "His underlying immunocompromised condition kept his body from getting rid of the virus,” the ministry said.

The patient returned to the hospital with a fever on 11 October and again tested positive for the MERS virus. Experts at the Korea Centers for Disease Control and Prevention (KCDC) concluded that some minimal amount of genetic material from the virus (MERS is the disease) had remained dormant in the patient's body, according to a health ministry press releases. Despite believing there was little risk of transmission, the KCDC put 61 contacts of the patient under home quarantine.

While hospitalized, the man alternately tested positive and negative for the virus. Meanwhile, his lymphoma progressed and caused his death on 25 November.  

South Korea's MERS outbreak stemmed from a single Korean man who carried the virus home after a trip to the Middle East. He sought treatment for a fever and before MERS was diagnosed on 20 May, the virus had spread among health care workers and patients at several different hospitals. The outbreak caught the South Korean health sector by surprise. Hospitals were slow to identify and isolate those infected. And health authorities stumbled in their initial efforts to trace contacts and enforce quarantines. But controls eventually worked. There were no new confirmed infections after 4 July. Korean Prime Minister Hwang Kyo-ahn declared a "de facto end" to the outbreak, on 28 July. But by then it had become by far the largest outbreak outside the Middle East with 186 laboratory-confirmed infections and 36 deaths.