Mers coronavirus has killed five more people in Saudi Arabia, taking the death toll due to the virus to 168 since September 2012, the Health Ministry was quoted as saying.

The ministry said nine more confirmed cases of Mers were reported, bringing the total number of infected cases to 629 since the outbreak of the chronic disease, said the Arab News report.

The latest fatalities are three patients from a government hospital in Jeddah, one from Riyadh and one from Madinah. The two others are a 71-year-old man in Riyadh and a 77-year-old man in Madinah.

Meanwhile, an Illinois resident tested positive for Mers after being in contact with an infected patient, though he did not show signs of illness, US health officials said.

The man likely contracted Mers from a man in Indiana who was hospitalised in late April with the first known US case of the illness.

The Illinois resident's lack of symptoms may shed light on milder forms of the deadly virus, which emerged in the Middle East in 2012 and has infected more than 500 patients in Saudi Arabia alone. It kills about 30 percent of those who are infected.

Researchers at the forefront of the global Mers response said this week they were investigating whether people infected with Mers who have no symptoms could still pass the virus on to others.

"There is evidence there is a broader spectrum of Mers" than first expected, said Dr David Swerdlow of the US Centers for Disease Control and Prevention, who is leading the US response to Mers.

The Illinois resident did not seek or require medical care and is reported to be feeling well, but officials involved in investigating the first case have been monitoring his health since May 3. A blood test on Friday showed he had developed antibodies to Mers. - Reuters