HOUSTON  — A suburban Houston woman has tested positive for the new coronavirus after flying home from Italy, prompting health officials on Tuesday to tell everyone who shared the business/first class sections on the two flights with her to self-isolate and call their doctors.

The woman, who is in her 20s, had been living temporarily in Italy, now one of the hottest COVID-19 infection zones, and flew back in business/first class on March 3 to consult her own doctor. County officials are appealing to everyone who sat in that section on Lufthansa Flight 309 from Florence, Italy, to Frankfurt, Germany, and on United Flight 47 from Frankfurt to Houston on March 3 to self-isolate and call their doctors.

The woman is the latest positive test to be announced in Texas. For most people, the new coronavirus causes only mild or moderate symptoms, such as a fever and cough. For some, especially older adults and people with existing health problems, it can cause severe complications, including pneumonia.

The vast majority of people recover from the new virus. According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe illness may take three to six weeks to recover. In mainland China, where the virus first exploded, more than 80,000 people have been diagnosed and more than 58,000 have so far recovered.

The wife and 3-year-old child of a North Texas man found to have the new coronavirus following a trip to California have also tested positive, health officials said Tuesday.

Texas has now more than two dozen confirmed cases of COVID-19. That does not include cases brought in from Wuhan, China, and two cruise ships for quarantine at Joint Base San Antonio-Lackland in San Antonio. About 380 passengers from the Grand Princess began arriving Tuesday night in San Antonio.

The family lives in the Dallas suburb of Frisco, and all were in stable condition and under self-quarantine at their home, Collin County Health Care Services said in a statement. Another child in the family was also being re-tested. The father is believed to be the first person in Texas to contract the virus within the U.S.

Dr. John Hellerstadt, commissioner of the Texas Department of Health and Human Services, said Tuesday that he could not provide lawmakers with the number of people tested for the virus in the state. Texas Gov. Greg Abbott has also asked health insurers to waive costs related to diagnosing the virus for families who are on state-regulated insurance plans.

A dozen cases around Houston have all been related to travelers on an Egyptian cruise.

In Montgomery County, located just north of Houston, health officials said Tuesday that a man in his 40s who was being treated at a local hospital tested positive. Officials said he’s a Montgomery County resident and that they are gathering details on his travel history.

Tarrant County also reported its first case Tuesday, described as a person who had recently traveled to a conference in Kentucky. The county provided no other information.

Also Tuesday, Dallas County reported its first positive case, a 77-year-old from out of state. The person, who has an extensive travel history, is being treated at a Dallas-area hospital. Later, county officials reported that a person close to the 77-year-old, this one aged in the 50s, also had tested positive.

The Northeast Texas Public Health District on Tuesday reported a case in Gregg County. That patient, who traveled within the U.S., was isolated at home.

Collin County officials said the father was in his 30s and is believed to have been exposed to the virus during a trip to Silicon Valley in February. The county said the family’s children had no symptoms and were not contagious while attending school.

In Austin, the MotoGP racing series on Tuesday postponed the annual Grand Prix of the Americas that was scheduled for April until Nov. 15. Local organizers said MotoGP’s decision was based on global travel considerations and noted that many of the race teams are based in Italy.

“The risk of shipping everything here, having fans coming here, and then not having an event, that was too big a risk to take,” said Bobby Epstein, chairman of the Circuit of the Americas race track where the grand prix is held.

Meanwhile, the first planeload of passengers arrived at Kelly Field in San Antonio shortly after 8 p.m. Tuesday. The masked passengers deplaned to vehicles that whisked them to the adjoining Joint Base San Antonio-Lackland.

It was the first of two planeloads of ship passengers to make the deliveries Tuesday night. The U.S. Centers for Disease Control and Prevention said 380 Grand Princess passengers are expected to be quarantined at the base.

The 380 either live in Texas or surrounding states, San Antonio Mayor Ron Nirenberg has said.

More than 230 people, caught by the quarantine in Wuhan, China, or stranded by a quarantine aboard the cruise ship Diamond Princess in Japan, were repatriated to Lackland earlier this month. Eleven were isolated after they were diagnosed with the virus, the others have been released.