"How many people live here?", "Have you had contact with foreigners?", "Do you know the rules of hygiene to follow?": House by house, 28,000 Cuban medical students tirelessly repeat these questions, looking for possible cases of coronavirus.
In the Vedado district of Havana, Doctor Liz Caballero Gonzalez, 46, accompanies two students, responsible for traveling the same block every day, making a total of 300 families.
Only their white coats can distinguish them from the rest of the population.
Not their cloth masks, which have become the norm in the streets of the island, where most shops require customers to wear them.
Cuba, one of the last Latin American countries to close its borders to non-residents on March 24 - to preserve tourism to the end - recorded 186 cases of coronavirus, including six deaths. As a precaution, 2,837 people are hospitalized.
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It now counts on its medical network, above average, to halt the spread of the disease: according to the World Health Organization (WHO), the island has 82 doctors per 10,000 inhabitants, compared to 32 in France and 26 in the USA.
Doctors "very loved"
"We don't have the technology of the rich countries, but we have a highly qualified, united, altruistic human staff," says Liz Caballero Gonzalez proudly.
This door-to-door "is nothing new": "the family doctor (paid about 50 dollars per month, note) always makes the round of his patients, to look for any communicable disease".
But "15 days ago, we started to do it in a more determined way, with 100% of the population".
Students are involved in this country which has 25 medical schools and a prestigious Latin American School of Medicine (Elam), where thousands of foreign students are trained.
"We were already used to going door to door," said Susana Diaz, 19, in the second year of medicine.
"There is always a time, around September-October, when we do it about dengue. When the coronavirus situation got worse, the university offered to do it too."
Any suspected case of cough or fever is immediately reported to the district medical center, said Susana, always welcomed during her visits: "Many thank us for what we do".
The doctors are "very loved" here, confirms Maité Pérez, 30, who has just answered the student's questions. "It makes me happy because they take care of our health."
Mop in front of her door to clean the shoes, mandatory washing of clothes when returning, wearing a mask on each outing: Maité scrupulously respects all the instructions.
There is just one that is more painful to him: the prohibition of all bestowal, real torture for the Cubans. "I have one of these desires to take my mother in her arms, to kiss her, to hug her ... but we can't!"
Chlorine and fabric masks
For Carlos Lagos, 83, it has become a routine to see students parading at his door. "(They ask me) if I feel bad, if I have a fever, how I take care of myself," he explains, shirtless due to the heat.
Attention to the elderly, the most vulnerable to coronavirus, is crucial because 20% of Cubans are over 60 years old.
"Up until now, I feel good and I go out very little!" Says, behind the grille of her apartment, Dolores Garcia, 82, delighted to have a cloth mask: "It is someone who love me very much who brought it to me. "
In Cuba, under American embargo since 1962, we regularly lack everything, sometimes even soap. Instead of the hydro-alcoholic gel, it is a chlorine-based solution that the inhabitants pour on their hands.
And due to the lack of medical masks, many fabric them, like the 56-year-old, who is busy drying them in the sun.
"When I saw that at first people were walking on the street without a mask, I set to work to make it". Without "any experience" in sewing, she borrowed one as a model from a nurse.
Marina has already sewn fifty, which she has distributed to her neighbors, and is preparing to make others. Finally, "it's not rocket science!"