（ウイルス、感染、感染症が）広まる、拡散する、（感染が）拡大する
（感染の）拡大

spread
自動詞
名詞

be spread
他動詞のspreadを受動態にした形

Knowing who was the first case is key to understanding how the virus spread.
https://www.bbc.com/news/world-europe-52526554

COVID-19 is a new disease and we are still learning about how it spreads and the severity of illness it causes.
https://www.cdc.gov/coronavirus/2019-ncov/prevent-...
※米CDCの記述で、spreadの主語はitで、これはCOVID-19を受けているのだが、後続の "the severity of illness it causes" を読む限り、このCOVID-19はウイルスのことを指していることになるので、言語的にはいろいろと微妙なことになっている（混乱している）ことがわかる。

The virus is thought to spread mainly from person-to-person.
https://www.cdc.gov/coronavirus/2019-ncov/prevent-...

Since the first case of COVID-19 was identified in central China in December, the illness has spread across the world, leading to an outbreak that the World Health Organization has called a pandemic.
https://time.com/5800901/coronavirus-map/

The disease spreads primarily from person to person through small droplets from the nose or mouth
https://www.who.int/news-room/q-a-detail/q-a-coron...

WHO is assessing ongoing research on the ways that COVID-19 is spread and will continue to share updated findings.
https://www.who.int/news-room/q-a-detail/q-a-coron...

Mapping the Spread of the Coronavirus Outbreak Around the U.S. and the World
https://time.com/5800901/coronavirus-map/
※TIME記事の見出し。

It is supplemented with additional reporting by ABC News and updated daily to show the spread of the disease across Australia’s states and territories.
The data provides a guide to how Australia is faring in the fight against the spread of the coronavirus pandemic.
https://www.abc.net.au/news/2020-03-17/coronavirus...

Preventing the spread of the coronavirus
https://www.health.harvard.edu/diseases-and-condit...

※自動詞の場合、主語は「ウイルス」だったり「疾患」だったりする。

※名詞のspreadが取る前置詞はofで、ここまでは辞書通りだが、その後がoutbreakだったりpandemicだったりdiseaseだったりvirusだったりと、なかなかのカオスっぷり。