BERLIN (NYTIMES) - They call them corona taxis: Medics outfitted in protective gear, driving around the empty streets of Heidelberg, Germany, to check on patients who are at home, five or six days into being sick with the coronavirus.

They take a blood test, looking for signs that a patient is about to go into a steep decline. They might suggest hospitalisation even to a patient who has only mild symptoms; the chances of surviving that decline are vastly improved by being in a hospital when it begins.

"There is this tipping point at the end of the first week," said Professor Hans-Georg Kräusslich, head of virology at University Hospital in Heidelberg, one of the country's leading research hospitals. "If you are a person whose lungs might fail, that's when you will start deteriorating."

Heidelberg's corona taxis are only one initiative in one city. But they illustrate a level of engagement and a commitment of public resources in fighting the epidemic that help explain one of the most intriguing puzzles of the pandemic: Why is Germany's death rate so low?

The virus and the resulting disease, Covid-19, have hit Germany with a force: According to Johns Hopkins University, the country had more than 92,000 laboratory-confirmed infections as of midday on Saturday (April 4), more than any other country except the United States, Italy and Spain.

But with 1,295 deaths, Germany's fatality rate stood at 1.4 per cent compared with 12 per cent in Italy; around 10 per cent in Spain, France and Britain; 4 per cent in China; and 2.5 per cent in the United States. Even South Korea, a model of flattening the curve, has a higher fatality rate: 1.7 per cent.

"There has been talk of a German anomaly," said Professor Hendrik Streeck, the director of the Institute of Virology at the University Hospital Bonn. Prof Streeck has been getting calls from colleagues in the United States and elsewhere.

"'What are you doing differently?' they ask me," he said. "'Why is your death rate so low?'"

There are several answers to this question, experts say - a mix of statistical distortions and very real differences in how the country has taken on the epidemic.

The average age of those infected is lower in Germany than in many other countries. Many of the early patients caught the virus in Austrian and Italian ski resorts and were relatively young and healthy, Prof Kräusslich said.

"It started as an epidemic of skiers," he said.

As infections have spread, more older people have been hit, and the death rate - only 0.2 per cent two weeks ago - has risen, too. But the average age of contracting the disease remains relatively low, at 49. In France, it is 62.5, and in Italy 62, according to their latest national reports.

Another explanation for the low fatality rate is that Germany has been testing far more people than most nations. That means it catches more people with few or no symptoms, increasing the number of known cases but not the number of fatalities.

"That automatically lowers the death rate on paper," said Prof Kräusslich.

But there are also significant medical factors that have kept the number of deaths in Germany relatively low, epidemiologists and virologists say, chief among them, early and widespread testing and treatment, plenty of intensive care beds and a trusted government whose social-distancing guidelines are widely observed.

TESTING

In mid-January, long before most Germans had given the virus much thought, Charité hospital in Berlin had already developed a test and posted the formula online.

By the time Germany recorded its first case of Covid-19 in February, laboratories across the country had built up a stock of test kits.

"The reason why we in Germany have so few deaths at the moment compared with the number of infected can be largely explained by the fact that we are doing an extremely large number of lab diagnoses," said Dr Christian Drosten, chief virologist at Charité, whose team developed the first test.

By now, Germany is conducting around 350,000 coronavirus tests a week, far more than any other European country. Early and widespread testing has allowed authorities to slow the spread of the pandemic by isolating known cases while they are infectious. It has also enabled lifesaving treatment to be administered in a more timely way.

"When I have an early diagnosis and can treat patients early - for example, put them on a ventilator before they deteriorate - the chance of survival is much higher," Kräusslich said.

TRACKING

On a Friday in late February, Prof Streeck received news that for the first time, a patient at his hospital in Bonn had tested positive for the coronavirus: A 22-year-old man who had no symptoms but whose employer - a school - had asked him to take a test after learning that he had taken part in a carnival event where someone else had tested positive.

In most countries, including the United States, testing is largely limited to the sickest patients, so the man probably would have been refused a test.

Not in Germany. As soon as the test results were in, the school was shut, and all children and staff were ordered to stay at home with their families for two weeks. Some 235 people were tested.

"Testing and tracking is the strategy that was successful in South Korea, and we have tried to learn from that," Prof Streeck said.

A ROBUST PUBLIC HEALTHCARE SYSTEM

Before the coronavirus pandemic swept across Germany, University Hospital in Giessen had 173 intensive care beds equipped with ventilators. In recent weeks, the hospital scrambled to create an additional 40 beds and increased the staff that was on standby to work in intensive care by as much as 50 per cent.

"We have so much capacity now, we are accepting patients from Italy, Spain and France," said Dr Susanne Herold, a specialist in lung infections at the hospital who has overseen the restructuring. "We are very strong in the intensive care area."

All across Germany, hospitals have expanded their intensive care capacities. And they started from a high level. In January, Germany had some 28,000 intensive care beds equipped with ventilators, or 34 per 100,000 people. By comparison, that rate is 12 in Italy and 7 in the Netherlands.

By now, there are 40,000 intensive care beds available in Germany.

TRUST IN GOVERNMENT

Beyond mass testing and the preparedness of the health care system, many also see Chancellor Angela Merkel's leadership as one reason the fatality rate has been kept low.

Dr Merkel has communicated clearly, calmly and regularly throughout the crisis as she imposed ever-stricter social distancing measures on the country. The restrictions, which have been crucial to slowing the spread of the pandemic, met with little political opposition and are broadly followed.

The chancellor's approval ratings have soared.

"Maybe our biggest strength in Germany," said Prof Kräusslich, "is the rational decision-making at the highest level of government combined with the trust the government enjoys in the population."