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Coronaviruses are a family of viruses, some of which cause respiratory illness in humans. The virus exhibits a crown-like halo, when viewed under an electron microscope, which is how it got its name.

Coronaviruses have been found circulating among animals, such as camels, cats and bats and a few have jumped to people - a spread defined by epidemiologists as "zoonotic."

Prior to December 2019, there were six coronaviruses that were known to have circulated among people. Four cause about 25% of colds. One caused Severe Acute Respiratory Syndrome (SARS), a disease that emerged in China in 2002, and another that causes Middle East Respiratory Syndrome (MERS). SARS infected about 8,000 and killed about 800. MERS emerged in Saudia Arabia in 2012 and has sickened about 2,500 and killed about 860.

The viruses that cause SARS and MERS aren't easily transmissible between people, and public health officials have been able to control their spread. There has been no community spread of SARS since 2003, according to the World Health Organization ... SARS is thought to have originated in bats, then jumped to civet cats, and then to humans. MERS is believed to have passed from camels to humans.

In December, another coronavirus emerged that shared some of the same genes as SARS, and therefore has been named SARS-CoV-2019, by the WHO. The understanding of this virus, which causes the disease COVID-19, is evolving almost daily, as scientists have raced to understand how contagious it is, its incubation period, it's morbidity and mortality rate, and how it passes between people.

On Jan. 30, 2020, the World Health Organization declared 2019-nCoV, a coronavirus, a public health emergency of international concern and on March 10, declared it a pandemic. The last time it declared a pandemic was the swine flu in 2009.

AHCJ is introducing these pages to help reporters cover this emerging topic and will be updating these resources to reflect the latest science and data, as well as strong reporting on the subject.

If you have suggestions for this page, please email pia@healthjournalism.org.