Countries that a few weeks ago never expected to have to combat the new infectious disease are realising they likely can’t keep it out in today’s connected world. Popping up in disparate places, sometimes with no clear epidemiological links to the original outbreak in China, the virus is now all but impossible to stop, public-health officials and infectious-disease experts say.

Italy’s outbreak started with a delayed diagnosis of a man who wasn’t suspected of having the virus because he hadn’t been to China or in contact with anyone with symptoms. New cases reported in one day outside China exceeded the number of new daily cases in China for the first time, the World Health Organisation said Wednesday.

The same day, the US identified a patient in California who could be the first to be diagnosed in the country without a clear explanation for how the disease was transmitted.

Increased travel and trade over the past couple of decades have significantly accelerated the risk of global spread of disease. Airline passenger traffic has more than doubled since 2003, when there was an epidemic of another coronavirus, severe acute respiratory syndrome (SARS), which infected nearly 8,100 people, killing 774. International trade rose to $19.45trn in 2018 from $7.59trn in 2003, according to the World Trade Organisation.

All told, there have been nearly 82,300 cases of the disease, called Covid-19, in 46 countries, with 2,804 deaths, since the virus was identified almost two months ago, according to the WHO. Reports of deaths and the confirmation of new infections in seemingly random places – a case was even confirmed this week above the Arctic Circle – have raised the prospect of a world-wide contagion.

Read also: Should I fly or should I stay? – coronavirus travel tips

Yet how big an impact the virus ultimately has depends partly on how transmissible and deadly it turns out to be – factors that aren’t yet fully understood. In some ways, as the stock-market tumble suggests, that uncertainty is driving concern.

Right now, cases of infection are falling through the cracks as the virus speeds around the world faster than screening measures are implemented or updated. The new virus is particularly challenging for public-health officials because people who are infected and transmitting to others might have only mild flulike symptoms, or no symptoms at all, making them difficult to identify. That is what makes this virus such a threat: It spreads more easily and is milder for most than SARS or Ebola, yet at least for the moment appears deadlier than some other highly contagious diseases, such as seasonal flu.

The outbreaks in Italy, South Korea and Iran all started with a few cases and expanded quickly, suggesting that many mild cases contributed unseen to the spread, said Nils Daulaire, a visiting scholar at the Harvard TH Chan School of Public Health and Arctic University of Norway, and a former assistant secretary for global affairs at the US Department of Health and Human Services.

“It is now a near certainty that it will spread to all corners of the globe and affect every country,” Dr. Daulaire said. “The horse is most decidedly out of the barn.”

Public-health systems around the world have improved their ability to detect and battle new emerging diseases, applying lessons learned from SARS, flu epidemics and a devastating Ebola epidemic in West Africa in 2014. Governments and other funders have also invested in new technologies to speed the development of medicines and vaccines.

But the new coronavirus epidemic shows that major gaps remain. Many countries still don’t have the staff or laboratory technologies to detect outbreaks quickly. Problems with diagnostic tests and protocols for the new coronavirus mean many infected people likely aren’t being tested. Few countries, including the U.S. and European nations, have extra supplies of hospital beds, ventilators or other equipment to handle an influx of patients with pneumonia caused by the new coronavirus.

“There has to be a shift in mind-sets,” said Bruce Aylward, a veteran epidemiologist who headed an international mission of experts for the WHO to China last week. “Have you got 100 beds where you can isolate people if you have to? Have you got a wing of a hospital that you’re going to close off?” he said.

While a lockdown in Hubei province in China has likely slowed the spread of the virus, millions of people left before it was imposed, and people who were infected and not diagnosed could have spread the virus elsewhere, experts say. Officials say the epidemic in China peaked a few weeks ago and new cases are on the decline.

“Pandemic” is defined by the WHO as widespread transmission globally of a new disease, taking a toll on society. The term has been applied to only a few diseases in history – a deadly flu in 1918, the H1N1 flu in 2009 and HIV/AIDS among them. The WHO’s director-general, Tedros Adhanom Ghebreyesus, warned earlier this week that while the new virus didn’t yet qualify as a pandemic, it “absolutely” could become one.

Read also: SA will not escape effects of coronavirus

The WHO is helping African nations and other countries prepare by sending out diagnostic test kits and other supplies, and training health workers. The agency is urging countries to be ready and says a pandemic can still be averted.

The US government said this week that it was operating on the assumption that the new coronavirus would spread in the country, and urged Americans to prepare for “social distancing measures” such as closing schools and canceling large-scale events.

Italy had moved aggressively to prevent a Covid-19 outbreak, initially screening travellers and then banning direct flights from China—the only country in the European Union to do so. Authorities had also quickly isolated two Chinese tourists who fell ill.

However, hospitals were told to test only patients who showed symptoms and who had been to China or in contact with other infected people. That was the protocol even though a British citizen had recently spread the virus after a trip to Singapore, and he showed no symptoms at the time.

When a 38-year-old man from Codogno, a town south of Milan, developed a cough and a fever on Feb. 15, it didn’t seem possible that he might be infected with the new coronavirus. The man, whose first name is Mattia and whose surname can’t be published under Italian privacy laws, had never been to China. He hadn’t had contact with people who showed symptoms of infection either, Italian health officials later said.

On. Feb. 18, Mattia, who works at a local research and development unit of Unilever, felt sicker and went to his local hospital. Doctors gave him antibiotics and he went home.

The next day he was admitted to the hospital in critical condition. Doctors tested him for the coronavirus after his wife told them he had met with a friend who had recently returned from China. On Feb. 20, health authorities confirmed Mattia had Covid-19.

Italian authorities moved quickly to track down and test people who had come into contact with Mattia or with his friend. Residents of Codogno and surrounding towns were told to stay at home.

It was too late. Tests showed the virus had spread. The infected included his pregnant wife and six members of his amateur soccer team. Medical staff and other patients at the hospital in Codogno had also been infected.

However, the friend who had returned from China tested negative.

So far 650 people have tested positive for the virus in Italy, of whom 17 have died, according to government data. Italy is struggling to contain the biggest public-health crisis in its recent history. “The country is facing this kind of emergency for the first time,” Prime Minister Giuseppe Conte said Tuesday.

Italian authorities are still trying to figure out how Mattia got infected. They suspect that one or more people with mild symptoms were unknowingly transmitting it for some time, according to Massimo Galli, head of the infectious-diseases department at Milan’s Sacco hospital, where many of the infected patients are being treated.

Ten towns in the Lombardy region and one in neighbouring Veneto have been quarantined, with armed forces manning checkpoints; supermarkets and pharmacies are the only stores open. The government has shut down schools, universities and cinemas across northern Italy. Several soccer matches were postponed and Venice’s annual carnival was curtailed. Some 27 million people live in areas affected by the restrictions.

“I was expecting the coronavirus to arrive in a big city, not in a small town,” says Leyla Bicer, a 35-year-old pharmacist from the quarantined town of Casalpusterlengo who serves customers through an 8-inch opening in the front door.

The current government policy is to test only people who show symptoms. Those who are infected are either admitted to a hospital or told to stay at home, provided they can be kept in isolation.

Carlo Benuzzi, who used to go running with Mattia, said none of the roughly 40 people who are part of their running group have been tested for the virus. “For the time being we are all well. Let’s hope it stays that way,” said Mr. Benuzzi, 56, as he stocked up on food supplies at a supermarket in Codogno.

More cases linked to the Lombardy outbreak have emerged elsewhere in Europe—from Sicily to Switzerland to Spain’s Canary Islands – raising fears it might be too late to stop it from spreading across the continent. A 56-year-old Italian woman vacationing in Austria died on Tuesday night.

Italy’s European neighbours have said that they will keep borders open and continue to allow Italians to travel. But checks and other precautions have proliferated, as well as pressure to cancel events.

The European Commission has called for member states to review their pandemic plans, including procedures for tracing the movements of patients. In Europe, the job of responding to epidemics rests with individual states. That along with social factors would make it difficult for Europe to replicate measures that China imposed, such as large-scale lockdowns, experts say.

Jeremy Farrar, director of the Wellcome Trust, a large medical-research charity, said the key is keeping containment efforts going as long as possible, to reduce overlap with flu season. The continent’s health systems are already under pressure, he said: “There isn’t a huge amount of spare capacity in the European health systems.”

Delaying the spread of the virus also buys time for doctors to test potential treatments for the virus, said Pasi Penttinen, principal expert at the European Centre for Disease Prevention and Control.

Holy city

In Iran, the more than 100 confirmed cases include Iraj Harirchi, the country’s deputy health minister and head of its coronavirus task force. He appeared feverish, mopping his face during a press conference this week, with a government spokesman standing next to him. A prominent reformist lawmaker also contracted the virus.

Iran has close ties with China, and Iranian authorities have said the virus was most likely introduced to the country directly from there. One reason that Iran now suffers from a shortage of masks is that Tehran donated a million of them earlier this month to China. Current U.S. sanctions have hampered imports of certain supplies and medicines.

The city of Qom, which officials have pinned as the epi-centre of the outbreak in the Islamic Republic, is one of the holiest cities in Shia Islam and attracts thousands of visitors every year. Religious rituals in the city include kissing and touching the shrines, and crowds praying while crammed together inside mosques.

Qom rivals Tehran in political power. Despite orders from the Iranian government to close shrines and mosques in Qom, clerics in the city resisted for days after the first Covid-19 case was announced on Feb. 19. Even after Iranian authorities canceled a three-day religious festival known as I’tikaf, scheduled for early March, Qom residents have openly defied orders from the governor’s security council to keep shrines closed.

Iraq, Kuwait, Oman and Afghanistan reported their first cases this week, linking them to Iran. Pakistan reported its first two cases and said both had traveled to Qom.

In South Korea, officials are reporting more new cases with no ties to a megachurch where the country’s large outbreak began. Around half of South Korea’s 2,022 confirmed patients have ties to the Shincheonji Church of Jesus. New clusters of infection have been reported at other churches, while one new cluster of potential infections is being examined at a hospital in northwest Seoul.

Citizens and physicians’ groups have criticised President Moon Jae-in’s administration for not banning the entry of Chinese nationals. On Wednesday, South Korea’s Health Minister Park Neung-hoo said 2,000 Chinese enter the country every day and quarantining them would be impossible. Mr. Park said the culprits for the country’s coronavirus cases were South Koreans who had traveled to China.

Health officials say they expect the number of confirmed patients to keep growing. The Seoul government has capped exports of surgical masks through the end of April amid short supply. It moved the prime minister to the hard-hit city of Daegu to run an anti-disaster headquarters. Individuals who refuse to be tested for coronavirus can be fined as much as 3 million South Korean won, or around $2,500.

Dr. Tedros, the WHO director-general, warned this week that using the term “pandemic” unless the disease was truly widespread globally could amplify fear and stigma and hamper efforts to stop it. Still, he said, “All countries, whether they have cases or not, must prepare for a potential pandemic.”

Write to Betsy McKay at [email protected] and Margherita Stancati at [email protected]