Pushing through the emergency department's rubber-coated swing doors, Dr Luiz Sérgio Verbicaro threw open his arms as if welcoming guests to his new home.

Before him a huddle of bored-looking medics made small talk around a table in a corner of the otherwise empty department. Outside, the ambulance bay was deserted.

"It is good – and abnormal," said Verbicaro, 60, a veteran surgeon and the director of the Getúlio Vargas hospital in northern Rio de Janeiro, until recently considered the Latin American champion in gunshot wound cases. "It is a relief."

Once upon a time, the flow of bloodied and disfigured gunshot victims made the Getúlio Vargas team a global reference point in bullet wound treatment – a ghoulish case study in the devastating impact of guns; a warzone hospital, without the war. More than 3,000 cases have been admitted in the last five years, an average of 50 a month. In 2007, the most violent year on record, 767 bullet-wound victims were brought in. Last year there were 583.

"It reached a point where on a 12-hour weekend shift … we'd receive an average of five gunshot victims. That was our routine," said Verbicaro, an Air Force reservist, whose hospital is flanked by what were until recently some of South America's most violent slums. "Often we couldn't even leave the hospital … because of shoot-outs."

But not any more. Doctors say a fledgling government drive to "pacify" Rio's slums – by ridding every favela of heavily armed drugs gangs by the time the city hosts the 2016 Olympics – has sent the number of gunshot patients into freefall.

In the wake of a massive military operation in November, in which security forces stormed and permanently occupied two vast favelas near the hospital, the number of bullet wound admissions at Getúlio Vargas has dropped almost 50%. In February there were 29 cases of what doctors call "PAFs" – firearm perforations. In the first 11 days of March there were just four.

"Compared with how things were it is fantastic: what we used to get in one week we are now getting in one month," said Dr Maria Cristina Lopes, head of the emergency department.

"Victims were arriving around the clock. It wasn't just at night or on weekends – it was every day. Since the occupation the drop has been very noticeable."

The calm came at a price. In November, when over 1,600 members of the security forces swept into the shantytowns, clashing with traffickers, 94 gunshot victims were admitted, among them a Reuters photographer and Rosângela Barbosa Alves, a 14-year-old student who was shot in the chest in a gunfight near her home.

Lopes, who watched her team fight in vain to save Alves, said she had been the last child brought in with a gunshot injury. "There's nothing worse than seeing a child die of a stray bullet," she said. "Children are not born to die children."

Even now the department is not a place for the faint-hearted. Victims of motorway crashes are common and horrific gunshot injuries continue to appear, albeit with less frequency. Earlier, the surgeons treated a 32-year-old man who was rushed in by highway police with multiple gunshots to the head and chest. "Liver injury. Chest drain. Jaw fracture," listed Verbicaro, leafing through the patient's sky-blue medical chart. "He's OK. It must have been a pistol."

But the changes are palpable. During the Guardian's last visit to the hospital, in 2008, 12 victims had been carried into the so-called "Red Room", including a three-year-old boy with shrapnel wounds, a policeman with burns to his face from a hand grenade and a 21-year-old man, shot in the head and bundled through the hospital's guarded entrance in a blood-stained duvet.

This time, Verbicaro toured the hospital showing off recent improvements – a new lick of paint, a new chapel for family members, a new tomography machine.

Asked what she expected from the rest of her shift, Lopes replied: "Tranquillity."

The 46-year-old paediatrician even hoped that the hospital's calmer routine might help her quit smoking.

"I'll get there," she said, an almost full pack lying on her desk. "As the stress levels go down so will the quantity of cigarettes."