A 55-year-old Chinese man living near Beijing was diagnosed with the Wuhan coronavirus on Thursday, almost two weeks after he was hospitalized with a fever. Three previous tests had indicated he did not carry the Wuhan virus, but the fourth test confirmed he did.

The South China Morning Post (SCMP) on Monday quoted China’s health commission stating that up to three tests are often needed to confirm the presence of the Wuhan virus in patients. A dismaying number of Chinese travelers have been arriving at airports around the world with Wuhan infections that are caught during airport screening for the infection.

The patient described by the SCMP is a railroad worker who lives in Tianjin, a huge city close to Beijing. A total of 28 coronavirus cases have now been detected in Tianjin. The man was reportedly quarantined in his home after he first checked into a local hospital with a fever on January 19, even though the first tests for the Wuhan virus came back negative, thus minimizing his contact with other people.

As of Monday morning, the coronavirus has been detected in 17,491 patients and is believed responsible for 362 deaths. The SARS outbreak of 2002-2003, to which the Wuhan virus is frequently compared, infected 5,327 people in mainland China and killed 349 of them. As these numbers suggest, the Wuhan virus is much more infectious than SARS but also much less likely to kill its victims.

The Wuhan virus is particularly insidious because infected people can be contagious for up to two weeks without displaying any outward symptoms. The SCMP recounted the case of a German businessman who got sick on a flight back from China, seemingly recovered after a few days, but then tested positive for the Wuhan virus after one of the people he met with in China grew ill and tested positive.

Wired reported on Saturday that epidemiologists are worried about “super-spreaders,” people who carry the Wuhan virus and can infect others while going for exceptionally long periods without experiencing any sign of illness. Super-spreading is difficult to monitor because the spreaders do not feel sick, so they might not seek medical treatment, making it difficult to trace chains of infection back to them. A larger number of people who carry the virus without any symptoms of illness could be one reason why the Wuhan virus is spreading so much more rapidly than SARS.

Politics could be another reason. Al-Jazeera noted on Monday that people in Wuhan are furious at the Chinese government for downplaying the severity of the viral outbreak and giving false assurances that the situation was under control.

As recently as last week, incredulous residents of Wuhan reported seeing propaganda from the Chinese Communist Party that hailed the government for a “transparent and swift” response that “highly impressed” international observers and supposedly contained the epidemic. Angry people in the outbreak area used social media to complain about slow medical responses, overwhelmed hospitals, and a media blackout that lasted until just a few days before the entire province was placed on lockdown.