World Health Organization (WHO) officials are worried about further spread of the coronavirus as untraceable cases pop up outside mainland China, where the outbreak originated.

The inability to identify the first patient in mini-outbreaks outside China has officials concerned that the virus may be spreading too quickly for standard public health measures to be effective.

“A number of spot fires, occurring around the world is a sign that things are ticking along, and what we are going to have here is probably a pandemic,” Ian Mackay, who studies viruses at Australia's University of Queensland, told Fox Business.

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For weeks now, China has quarantined the city of Wuhan, the epicenter of the outbreak, and more than a dozen other cities, affecting 60 million people.

The WHO said new clusters of the virus in Iran and South Korea could signal that it is becoming uncontainable.

“What we see is a very different phase of this outbreak depending where you look,” Dr. Sylvie Briand told Fox Business. “We see different patterns of transmission in different places.”

A global pandemic, as defined by the WHO, is a disease that spreads on at least two continents.

The biggest concern for officials has been Iran, where there are now 28 new cases, with five deaths, in a matter of days. The hotspot started in the city of Qom, but it's unclear how. Infected travelers from Iran have surfaced in Lebanon and Canada.

The U.S. has 35 reported cases of the virus, but no deaths.