Coronavirus may have hit China in fall, long before cases were first confirmed in December 2019: Satellite data
A substantial increase in parking lot traffic outside Wuhan hospitals last fall, coupled with an increase in internet searches for coronavirus-like symptoms, suggests that Covid-19 could have hit China way before it was first detected and confirmed in December 2019. This is according to researchers from Boston University School of Public Health; Boston Children’s Hospital and Harvard Medical School, who analyzed hospital traffic and search engine data in Wuhan and found early disease activity in the fall of 2019.
Satellite imagery and internet search trends have previously been harnessed for respiratory disease surveillance. According to experts, these sources are early indicators of epidemics and are sensitive to trends that may otherwise go undetected by traditional public health surveillance mechanisms. In this study, the research team used two of these previously validated data streams to look for indicators of potential Covid-19 disease before December 2019.
The researchers identified six hospitals for imagery analysis: Hubei Women and Children’s, Wuhan Tianyou, Wuhan Central, Wuhan Tongji Medical University, Wuhan Union and Zhongnan Hospital of Wuhan University. They also identified high traffic areas, including the Huanan Seafood Market and two railway stations (Wuchang and Hankou) for validation. Overall, they collected 111 satellite images of Wuhan (multiple sites per image) from January 9, 2018, to April 30, 2020, resulting in 140 successful daily extractions of parking lot volume from hospitals and 117 from the three high-volume control sites.
The analysis shows a dramatic increase in hospital traffic outside five Wuhan hospitals and search volume beginning in late summer and early fall 2019. On October 10, 2018, for example, there were 171 cars in the parking lot of Tianyou Hospital, but a year later, satellites recorded 285 cars, suggesting an increase of nearly 67%. Other hospitals showed up to a 90% increase when comparing traffic between the fall of 2018 and 2019, says the study. The researchers also found that in August, there was a “unique increase in searches” for diarrhea, which was neither seen in previous flu seasons or mirrored in the cough search data. The increase of both signals “precede the documented start of the Covid-19 pandemic in December,” highlighting the value of novel digital sources for surveillance of emerging pathogens, says the team.
The researchers acknowledge that they cannot confirm if the increased volume was directly related to the new coronavirus. However, they say that their evidence supports other recent work showing that emergence happened before identification at the Huanan Seafood market. These findings also corroborate the hypothesis that the virus emerged naturally in southern China and was potentially already circulating at the time of the Wuhan cluster, they add.
“(The analysis shows) a steep increase in parking lot volume starting in August 2019 and culminating with a peak in December 2019. Individual hospitals have days of high relative volume in both fall and winter 2019. However, between September and October 2019, 5 of the 6 hospitals show their highest relative daily volume of the analyzed series,” says the researchers in a pre-print. They add, “While searches for “diarrhea” only show elevated traffic starting in late 2019, “cough” shows yearly peaks that approximately coincide with influenza season. Both search query terms show a large increase approximately 3 weeks preceding the large spike of confirmed Covid-19 cases in early 2019.”
The team says that while surprising, this finding lines up with the recent recognition that gastrointestinal symptoms are a unique feature of Covid-19 and maybe the chief complaint of a significant proportion of presenting patients. “This symptom search increase is then followed by a rise in hospital parking lot traffic in October and November, as well as a rise in searches for cough. While we cannot conclude the reason for this increase, we hypothesize that broad community transmission may have led to more acute cases requiring medical attention, resulting in higher viral loads and worse symptoms,” says the study.
In December 2019, an outbreak of apparently viral pneumonia of unknown cause emerged in the city of Wuhan, in the Chinese province of Hubei. On December 31, 2019, the World Health Organization (WHO) China country office was informed of the cases detected in Wuhan. On January 9, 2020, the Chinese health authorities and the WHO announced the discovery of the novel coronavirus, which was confirmed as the agent responsible for the Wuhan cases
According to the research team, the initial rise in gastrointestinal symptoms may also hint at the missed early signals of Covid-19 in current surveillance systems for respiratory pathogens. “The standard definition for influenza-like illness is a combination of fever along with cough and/or sore throat. This narrow definition, which has focused on the detection of influenza transmission, would have missed milder cases with a different symptom mix that also could include loss of taste and smell. This finding also hints at the need to broaden surveillance efforts to consider novel pathogens that might display a range of unexpected symptoms,” they recommend.
The team says while further research is needed to validate the emergence of SARS-CoV-2, this study adds to a growing body of work on the value of digital sources as an early indicator of a disease outbreak in the context of limited integrated electronic surveillance data. “While not a replacement for more traditional methods, these data can help supplement other sources to provide a richer situational awareness picture of social disruptions, including those caused by a novel respiratory virus,” say researchers.