According to the prevailing understanding as well as WHO guidelines, COVID-19 transmits through mostly droplets, with contaminated surface and aerosol being much less frequently. A very recent cluster in Qingdao, China didn’t change that narrative, yet added significantly new data and important implications.
It started like a detective story (https://news.sina.cn/gn/2020-10-16/detail-iiznctkc5948642.d.html). On Sept 24, 2020 two dock workers at the Qingdao seaport tested positive and were asymptomatic. They were identified through routine surveillance of people with certain occupations, in their case, handling imported, frozen meat and fish products. For two weeks nothing else happened. Then since Oct 11, 2020, 12 more people tested positive, all associated with the Qingdao Chest Hospital: most are hospitalized patients with existing lung illness there, some were their care workers, one close contact. They were initially identified through screening of all hospitalized patients. As the same hospital also treats traveler-patients returning from overseas, the first suspicion was that the 12 cases were linked to those travelers. But it turned out that the two aforementioned dock workers took CT scans at the hospital, and the next morning two of those 12 went to the same CT room. So the evidence strongly indicated that the dock workers transmitted COVID-19 to patients at the hospital. Viral sequencing supported the link as well. On Oct 14 one of the two dock workers became symptomatic, while the other is now negative. On Oct 17, the Chinese CDC announced isolating live virus from the frozen food packages at the Qingdao port (https://news.sina.com.cn/c/2020-10-17/doc-iiznctkc6123590.shtml). The chain of transmission is established as follows: the dock workers were infected by virus on the food packaging, they took CT scan, the CT room was not cleaned thoroughly, and people at the hospital were infected.
There is a lot of information to digest here. The most significant is likely it is the first time live virus has been recovered from frozen food packages, transported over a long distance and for days or even weeks. While it is still formally possible the dock worker(s) being infected elsewhere and then contaminating the food packages, this is highly implausible. The last time the two workers transporting the goods was on Sept 19. So testing positive on Sept 24 is consistent with the timeline of COVID-19 transmission and progression, while one of the two didn’t develop symptoms until weeks later. In other words, they couldn’t have been infected early enough to contaminate the goods. Because of routine testings, they were identified quickly, but their family members, coworkers, and other close contacts are all negative, hence no evidence anybody infected them. Lastly, environment associated with imported frozen goods like seafood has tested positive around China for months, and even suspected in sporadic outbreaks before (e.g., Aug 6, 2020 blog). Live virus was not recovered then, so sources of those outbreaks remain undetermined. But getting live virus this time shows that, at least in the Qingdao case, virus can persist on contaminated frozen goods for a long time and infect people. So this is no longer a theoretic possibility. It doesn’t happen often: if a country has >10K infections per day, people don’t need to pay attention to it. But if any country wants to suppress COVID-19 close to 0, it must look at all the loopholes.
Next, how did the dock workers transmit the virus through the CT room? It is not clear when they took the CT, but they likely have been isolated at the hospital since Sept 24 and taken multiple CT scans. Apparently other patients used the same room the next morning. Assuming the hospital staff always cleaned the CT machine and room (although not well enough), the dock workers must have left a great deal of virus everywhere or highly concentrated somewhere. Without more information on the timing and inside the CT room, it is hard to know what happened. Oct 11 was the first date additional infections were identified, so perhaps Oct 6 was when the doc workers took the CT; because one dock worker became symptomatic on Oct 14, it is safe to assume he was asymptomatic on Oct 6. Can someone asymptomatic produce so much virus to contaminate the environment that infect others the next day? Declaring symptoms is often subjective, but passing CT scan at least says the lung is mostly normal. Moreover, was it transmission through contaminated surface or aerosol? Aerosol probably doesn’t last overnight, but surfaces should be dry as well, unless how they cleaned the place was problematic. Indeed, there are a lot of interesting questions here.
When Wuhan had the first outbreak, people took CT like candies, especially when RNA testing was limited in Jan. With what we now know about Qingdao, one wonders how many people in Wuhan got infected by taking CT, when the CT rooms were much more crowded than in Qingdao? Furthermore, hospital transmission was the culprit in the April Heilongjiang outbreak as well, although not the CT room. All these raise an alarm bell at hospitals. It should be noted that all the doctors and nurses (hundreds) at the Qingdao Chest Hospitals have tested negative, so good personal protection helps.
The last important observation is that one dock worker tested positive on Sept 24 (likely infected on Sept 19) but turned symptomatic only on Oct 14, with a lag longer than usual. Still, he might have very mild symptoms before Oct 14, and we don’t know when his last “normal” CT scan was. But it is indeed prudent to monitor every infected person to make sure he turns negative, regardless of time.
BTW, in light of the cluster, Qingdao tested its whole 10 million people in 6 days. It was a pool test, but still amounted to 0.5-1 million individual tests. All in all, it found the 12 cases, all associated with the Hospital. In essence, Qingdao found 0 cases in the broad population, i.e., 0 for 10 million. Just like the May Wuhan test, June Beijing test, etc, another giant waste of time, effort, and materials. The only good thing coming out of this folly is perhaps just to remind people no COVID-19 fatigue, once in a while. Since there is not much going on in China.
In summary, finding in Qingdao reveals an infrequent but nevertheless hugely important route of COVID-19 transmission. Not only can human travelers spread the virus, so can transported, frozen goods. The latter must have had caused an unknown number of unexplained outbreaks around the world. CT machine or room, like any indoor space, should also be taken seriously.
