Two evacuees from the Diamond Princess who were quarantined at Joint Base San Antonio-Lackland are infected with coronavirus, and health officials said they expect more cases among the cruise ship’s passengers in the coming days.

So far, the Centers for Disease Control and Prevention has confirmed the COVID-19 virus in 18 people brought to the U.S. from the cruise ship. Two of them are among the 144 evacuees who came to Lackland on Monday for a two-week quarantine, Dr. Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, said in a call with reporters Friday.

Despite aggressive efforts to contain the cases that already have surfaced in the country, Messonnier said “it’s very possible, even likely” that person-to-person transmission eventually will occur in the U.S.

“This new virus represents a tremendous public health threat. We don’t yet have a vaccine for this novel virus, nor do we have a medicine to treat it specifically,” she said. “We may see poor outcomes in others, not just people who were on board the Diamond Princess, but among others who become sick with this virus.”

On ExpressNews.com: With release of Wuhan evacuees from Lackland, federal officials turn attention to cruise ship passengers

Kate Grusich, a CDC spokeswoman, said the infected passengers in San Antonio had tested positive for the virus before they were evacuated from Japan, results that were confirmed by CDC after they arrived at Lackland. They have been isolated and are receiving medical treatment nearby, she said.

At least a half-dozen of the cruise ship evacuees at Lackland were transported this week to hospitals for testing.

The new diagnoses bring the total number of confirmed coronavirus cases in San Antonio to three. All the infections affected evacuees who were quarantined at Lackland.

Conditions on the Diamond Princess had grown increasingly grim as the ship docked at a port in Yokohama, Japan, for an attempted self-quarantine, after a passenger was found to be infected. In the ensuing days, it would become home to the highest concentration of coronavirus cases outside China, including more than 600 infections. Two elderly Japanese passengers have died.

Several American passengers who are hospitalized in Japan are “seriously ill,” Messonnier said.

In light of those circumstances, and the close contact the passengers had on board with so many infected people, Messonnier said, the evacuated Americans “are considered at high risk for infection.”

The new cases include more than a dozen asymptomatic Diamond Princess passengers who unexpectedly tested positive for the virus as the State Department was in the process of evacuating 329 Americans from the cruise ship. A handful of the infected people traveled on the flight to Lackland but ultimately were taken to Nebraska for their treatment.

On ExpressNews.com: ‘Victims of circumstance’: Cruise ship passengers quarantined at Lackland faced chaotic trip home

Previously, coronavirus was diagnosed in an evacuee taken to Lackland from Wuhan, China, where the new pathogen first emerged.

The evacuee still is hospitalized in San Antonio. The patient initially was treated at Methodist Hospital | Texsan but was transferred to another facility after improving, said Jennifer McQuiston, a captain in the U.S. Public Health Service who led the CDC’s quarantine of the Wuhan evacuees.

It’s possible the evacuee, and the two other infected people, are under the care of the Texas Center for Infectious Disease, a state-run tuberculosis hospital in San Antonio that began treating an unspecified number of patients earlier this week. The hospital has set aside a separate 22-bed wing for people infected with the virus who are experiencing mild symptoms, as well as those who are suspected of having it.

The patient from Wuhan will not be released until nose and mouth swabs test negative for the virus at least two days apart, McQuiston said in an interview.

The other 90 Wuhan evacuees at Lackland were declared healthy and released at 9 a.m. Thursday, after a two-week quarantine at a hotel on the base.

As their departure approached, McQuiston said the atmosphere grew jubilant. Tears flowed, music played and McQuiston exchanged hugs with each evacuee, sans protective gear.

The group — which included many families and children who had also self-quarantined in Wuhan — was free to go outside for the first time in weeks.

That outcome, McQuiston said, “proved that quarantine works.”

“I have been so impressed with the resilience and the enthusiasm of our passenger group,” she said. “I’m so proud of them for coming through this.”

On ExpressNews.com: State hospital in San Antonio begins treating coronavirus evacuees from Lackland

However, McQuiston acknowledged several factors will complicate the still-ongoing quarantine of the Diamond Princess passengers.

On the ship, the passengers had a higher degree of exposure to the virus than those who came from Wuhan. Many also are older and may have underlying medical conditions that make them more susceptible to complications from the virus.

It’s also a much larger group that requires more federal resources, she said.

Already, protocols for testing have shifted from one group to the other. Not all the Wuhan evacuees were tested for the virus, McQuiston said, but the CDC will swab any cruise ship passengers who want to be tested.

With the Wuhan evacuees gone, McQuiston said she was headed home for a reprieve.

The Diamond Princess evacuees at Lackland are being overseen by Rear Adm. Nancy Knight, a medical doctor who serves as director of the division of global health protection at the CDC. Knight had worked on the quarantine of nearly 200 people at March Air Reserve Base earlier this month and previously responded to infectious disease threats in other countries, including the HIV epidemic in South Africa.

Local officials are having ongoing conversations with the agencies coordinating the quarantine at Lackland. Bruce Davidson, spokesman for Mayor Ron Nirenberg, said the mayor organized a meeting Friday morning with local, state and federal officials and hospital leaders to discuss a strategy for handling coronavirus cases.

Earlier this week, Nirenberg and other officials in San Antonio had raised concerns about safety risks posed by transporting evacuees from Lackland to local hospitals. City and county officials have asked that evacuees be kept at the base until a diagnosis is confirmed, a request that’s still pending, Davidson said.

Lauren Caruba covers health care and medicine in the San Antonio and Bexar County area. Read her on our free site, mySA.com, and on our subscriber site, ExpressNews.com. | lcaruba@express-news.net | Twitter: @LaurenCaruba