Transmission electron microscope image of the novel coronavirus, isolated from a patient in the U.S. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, crown-like.

OMAHA — Health officials have confirmed two more cases of COVID-19, the illness caused by the novel coronavirus, in Douglas County. That brings the state's total to 13.

The cases involved a man in his 50s and a woman in her 60s. Both had traveled recently, officials said.

Contact investigations are underway to determine who might have come in contact with the two.

All close contacts of the two will self-quarantine and be actively monitored twice daily by public health officials for fever and respiratory symptoms.

“The positive news is that our latest cases also are travel-related,” Adi Pour, the health department's director, said in a statement.

Nebraska Gov. Pete Ricketts said during a press conference Friday that health officials so far have not detected the spread of coronavirus within the state's communities.

Health officials say the best way to stop the spread of the virus is to wash your hands often, avoid sick people, stop touching your face and stay home if you are sick. People also should cover their mouth and nose with a tissue or use a sleeve if coughing or sneezing.

The Douglas County Health Department also is encouraging businesses, schools and the general public to consider limiting large gatherings, closing buildings and canceling or postponing events to help slow or stop the spread of the virus.

The elderly and those with underlying health conditions — people who are most at risk from COVID-19 — should avoid large crowds.

COVID-19 symptoms include a fever, a cough or trouble breathing. If you develop symptoms, you should contact your health care provider. Please call ahead before you visit a doctor’s office or a waiting room.

Douglas County Health Department’s COVID-19 Information Line is open weekdays from 8:30 a.m. to 4 p.m. at 402-444-3400 to answer general questions about this new disease. The line is answered in English and Spanish. The United Way’s 211 information line also is taking calls when the Douglas County Health Department line is closed.