  [Background] Two clusters of coronavirus disease 2019 (COVID-19) were
confirmed in Hokkaido, Japan in February 2020. To capture the clusters, this
study employs Web search query logs and user location information from
smartphones. [Material and Methods] First, we anonymously identified smartphone
users who used a Web search engine (Yahoo! JAPAN Search) for the COVID-19 or
its symptoms via its companion application for smartphones (Yahoo Japan App).
We regard these searchers as Web searchers who are suspicious of their own
COVID-19 infection (WSSCI). Second, we extracted the location of the WSSCI via
the smartphone application. The spatio-temporal distribution of the number of
WSSCI are compared with the actual location of the known two clusters. [Result
and Discussion] Before the early stage of the cluster development, we could
confirm several WSSCI, which demonstrated the basic feasibility of our
WSSCI-based approach. However, it is accurate only in the early stage, and it
was biased after the public announcement of the cluster development. For the
case where the other cluster-related resources, such as fine-grained population
statistics, are not available, the proposed metric would be helpful to catch
the hint of emerging clusters.
