Mpox, previously known as monkeypox, has been in the spotlight as Hong Kong has reported 26 infections since last month, or three-quarters of the total 34 cases in the city so far. More than half of the recent cases had no travel history, suggesting they were infected locally.

So far, the disease has been limited mainly to the city’s community of men who have sex with men.

The mainland saw 491 new cases in July and caught the attention of the WHO. It noted in its latest mpox report earlier last week that a “significant increase” in cases had been observed in the Western Pacific region, driven by “sustained community transmission” on the mainland.

Dr Siddharth Sridhar, clinical assistant professor from the University of Hong Kong’s department of microbiology, said the increase in mpox infections on both sides of the border followed the relaxation of pandemic-related travel measures late last year, even though the global surge of cases started last summer.

“With an increase in international travel, the at-risk population in Hong Kong and the mainland were more likely to be exposed to mpox,” he said. “If there is a sustained outbreak on the mainland, cross-border cases are to be expected.”

Last July, the WHO declared mpox a public health emergency of international concern after infections were reported in countries where the disease was not endemic. So far, 113 countries, mostly in the Americas and Europe, have reported cases. The global alert ended in May.

Dr Wilson Lam, the vice-president of the Hong Kong Society for Infectious Diseases, said he believed that the city and the mainland were not greatly affected at the start of the global surge in cases as the region was still shielded by pandemic-related travel measures.

Infections began turning up in the region when travel resumed.

Sridhar agreed that it was possible that more mpox cases might spread from the mainland to the city, but he did not think it would pose a major threat to overall public health.

“We have to be realistic. Apart from mpox, there are also other types of infectious diseases … as long as there is social interaction and cross-border travel, [transmission] could happen,” he said.

“The risk to the general population is low, it’s not possible to have a sudden community outbreak of mpox.”

Professor Kelvin To Kai-wang, chairman of HKU’s microbiology department, was concerned about the rapid rise in reported cases, with new ones logged almost daily over the past week.

In contrast, the city’s first eight cases appeared over a 10-month period starting in September last year.

“When there are more cases in neighbouring regions, naturally the chance of Hong Kong seeing more cases will be higher,” he said.

But infectious disease specialist Lam said the speed that the virus spread from one region to another depended on the networks of men who had sex with men. They accounted for all but one case in the city and made up the majority in the recent global outbreak.

He said contact between the local network and those on the mainland and overseas was infrequent, based on past studies on the spread of other sexually transmitted diseases. But he agreed that sexual contact between people from different geographical origins could not be ruled out.

Hong Kong health authorities warned last month of an outbreak among local high-risk groups following a surge of cases. A dedicated vaccination centre was set up, after a voluntary inoculation scheme was introduced last October.

To curb the spread locally, the government should follow international guidelines and allow mpox patients to isolate at home instead of in hospital as this would encourage people to get tested, Sridhar said.

He added that people might not seek medical attention knowing that if they tested positive for the virus, they would have to stay in hospital for weeks.

Hong Kong currently isolates mpox patients in public hospitals until “all infectious lesions are resolved” and they become non-infectious, without stating a specific period of time.

Sridhar said only mpox patients with more serious symptoms, such as intense pain, requiring medication needed to be hospitalised.

Businessman Kenneth Kwok, 31, said he had stayed in hospital for roughly two weeks last September after he was confirmed to be the city’s first mpox case, even though his symptoms were mild. He was released only when his lesions dried up, crusted over and fell off.

He had ulcers in his genital area, and rashes over his face, body and limbs but said it was “milder than acne”.

“I didn’t feel any discomfort … it was like I was occupying a hospital space for no reason,” he said.