Coronavirus testing data has been spotty and not easily available, especially in the United States. Based on official government sources, here’s how testing efforts in the United States compare with those in Italy and South Korea.

Delays in testing in the United States have set back the nation’s response to the pandemic, even though its first case was discovered around the same time that South Korea’s was. But part of the problem in the United States has also been gaps created by the way the state and federal agencies report the data.

An internet community effort, called the COVID Tracking Project, is attempting to provide a fuller picture of testing in the United States. According to the tracker — which collects information directly from state health departments, local news reports and live news conferences — at least 41,000 people have been tested in the United States, much higher than official C.D.C. figures.

Comparing Daily Testing Data in U.S. Sources: C.D.C.; the COVID Tracking Project

It has been difficult to track reliable testing data in the United States for a number of reasons. Data from the Centers for Disease Control, which lags several days, reports the number of specimens tested, not the number of people — multiple specimens can be tested from each person. And some states report only positive results, not negative ones, making it hard to know the total number tested.

The COVID Tracking Project’s data, however, lays bare just how behind the United States has been in responding to the pandemic, which by Monday night had sickened more than 178,000 people worldwide, according to official accounts.

Recent data shows that about 125 people per million have been tested in the United States — far fewer than most other countries where data is available.

Coronavirus Tests Per One Million People Note: Data is from country health departments where available. Press reports and statements were used otherwise. The U.S. estimate is based on the most recent data from the COVID Tracking Project

Through intensive testing and monitoring, South Korea has managed to slow the growth of new cases. Health officials there tracked down people with symptoms and even set up drive-through testing, allowing at least 10,000 people to be tested per day. Government websites and mobile apps disclosed how many people had been tested and where.

Italy has also tested aggressively for the virus, which could help explain why its total confirmed cases are higher than every other country in Europe. Health officials in Lombardy — Italy’s hardest-hit region — initially carried out swab tests on those who were sick as well as those who came into contact with infected people, even if they had no symptoms.

Until now, testing in the United States has been done manually, with individual labs performing only 40 to 60 tests a day. Testing has ramped up in recent days — on Monday, the COVID Tracking Project’s count of reported tests rose by 13,000, suggesting a surge in the nation’s testing.

Also on Monday, federal officials said they were moving ahead with plans to set up more drive-through testing centers around the country and to speed the processing of tests by commercial labs. By the end of the week, officials said that 1.9 million tests should be available.