January: 1994 Northridge Earthquake

Coccidioides fungus at the center of tissue sample from a person with Valley fever. | National Institutes of Health

There
was an unusual “side effect” of the 1994 Northridge earthquake: a major
outbreak of Valley fever in Ventura County, California.

Valley fever is a
respiratory disease, endemic to the United States’ Southwest and parts
of Central and South America. It is caused by Coccidioides
fungus, which grows in the upper few inches of soil. People develop
Valley fever after inhaling dust containing the fungal spores. Although
60% of people who inhale Coccidioides are asymptomatic, the fungus can cause a flu-like illness and very rarely can spread outside the lungs to other organs.

In the eight weeks
after the Northridge earthquake, there were 203 cases of Valley fever
reported in Ventura County—an order of magnitude more than the expected
number of cases for that region and that time of year. Three people died
from Valley fever, representing 4% of Northridge-related deaths.

So how were the
earthquake and outbreak connected? U.S. Geological Survey seismologists
Edwin Harp and Randall Jibson partnered with scientists from the U.S.
Centers for Disease Control and Prevention to solve the medical mystery.
Their initial suspect and eventual culprit: landslides. The earthquake
triggered more than 10,000 landslides in the area, with a large
concentration of them in the young, weakly consolidated material in the
steep-walled canyons of the Santa Susana Mountains. The researchers
found that the outbreak fit a temporal and spatial pattern of landslide
dust blown southwest from the mountains into Simi Valley. The dust was
visible from aerial reconnaissance flights, and Simi Valley drivers
reported using their headlights right after the earthquake to see
through the thick plumes.

KEEP ON READING

Read more about this month’s historic earthquake in key papers from SSA journals. The following papers will be available for free for two weeks, from 17-Jan-2023 to 31-Jan-2023.