By Nathan Layne and Caroline Humer

DANBURY, Conn., March 18 (Reuters) - Drive-thru coronavirus testing sites are starting to pop up across the United States but few if any are at the major retail stores that pledged last week to provide parking lot space for them.

On Wednesday, many Americans with suspected coronavirus infections were heading to drive-thru testing sites at hospitals, with their doctor's referral. They were met by healthcare workers in protective gear, swabbing their noses through an open window.

The goal is to ramp up testing, the lack of which has been a major obstacle to understanding the extent of the pandemic, reduce pressure on emergency rooms and keep patients in cars to avoid spreading the infection.

Leading U.S. retailers, such as Walmart Inc, Target Corp, Walgreens Boots Alliance and CVS Health Corp pledged at a White House news conference last Friday to provide space for the drive-thru sites in their parking lots.

Admiral Brett Giroir of the U.S. Public Health Commission told reporters in Washington on Tuesday drive-thru test centers were "blossoming all over the country." But he added the initiative had faced some early challenges.

The public health commission was "really pushing equipment" to 47 centers in a dozen states, after doing a trial run on Monday with public health staff in protective gear, Giroir said. About 140 U.S. public health staff would be deployed to the sites along with state health workers, he said.

"We had a lot of kinks in the system, as you can expect," he added. "That's why we do a test before we go out into the field ... They're going to be adapted to the state and the local situation, but we're very confident that these will add testing to the already very robust healthcare system."

CVS spokesman TJ Crawford said the pharmacy chain was preparing this week to launch a pilot drive-thru testing site in the parking lot of a Shrewsbury, Massachusetts, CVS Pharmacy. Initial testing would be limited to first responders and local healthcare professionals who are on the frontlines of treating the virus and preventing its spread, he said.

HOSPITAL APPOINTMENTS

For the time being, tests are mainly being conducted at hospitals.

About 80 people had visited the drive-up testing location at Danbury Hospital in Connecticut by late Wednesday morning, according to a police officer at the entrance to the site, which had been set up in a covered parking garage.

The testing site, one of a handful established at hospitals in Connecticut, was accepting people by appointment only. Some visitors who showed up without an appointment were directed how to make one and come back later, said the officer who did not want to be identified. "It has all gone pretty smoothly," he said.

A handful of other drive-thru tests at hospitals have started up in New York, Massachusetts, Ohio, Virginia, Colorado and California.

New Jersey on Friday will open its first large-scale drive-up testing site at Bergen County Community College in Paramus with capacity to take in 2,500 specimens a week, state health commissioner Judy Persichilli told a news conference.

Health workers at the sites will send the nasal swabs to labs, including commercial labs run by Quest Diagnostics and LabCorp, for testing, health officials at the news conference said. (Reporting by Nathan Layne in Danbury and Caroline Humer in New York Writing by Bill Tarrant; editing by Tom Brown)

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