The countries of Africa, like Indonesia, as of Tuesday had not yet reported a single confirmed case, though there have been many suspected cases. Africa, too, is a frequent destination for Chinese travelers — though most come to the continent for work, not tourism.

Five researchers at the Harvard T.H. Chan School of Public Health concluded in a study last week that Indonesia and Cambodia, which has reported only one case, should quickly intensify its monitoring of potential cases. Based on a statistical analysis, the disease could have arrived in Indonesia already, the authors concluded.

“Many of the imported cases have been linked to a recent travel history from Wuhan, suggesting that air travel volume may play an important role for the risk of cases being exported outside of China,” the study said.

The chairman of the Indonesian Red Cross, Jusuf Kalla, a former vice president of Indonesia, also said it was possible that the disease had already entered the country and that Indonesians might not recognize the symptoms as being coronavirus.

“Singapore has a tight system, but even there the virus got in,” he said. “It’s possible that there are infected people but here in Indonesia people think that it is only a regular fever or they think it is dengue fever.”

Mr. Kalla expressed concern about how prepared Indonesia was to handle the virus if it were to strike in remote parts of the archipelago nation where underfunded community health centers are the main health care provider. (Indonesia is the world’s fourth most populous country, with nearly 270 million people scattered across 6,000 inhabited islands.)