Brazil is bracing for a surge in coronavirus cases as doctors and researchers warn that underreporting and a lack of testing mean nobody knows the real scale of Covid-19’s spread.

“What’s happening is enormous underreporting,” said Isabella Rêllo, a doctor working in emergency and intensive care in Rio de Janeiro hospitals, in a widely shared Facebook post challenging official numbers. “There are MANY more,” she wrote.

As Latin America’s worst hit country, Brazil officially has 9,056 coronavirus cases – including actors, singers, government ministers and Fabio Wajngarten, press secretary of the president, Jair Bolsonaro.

With 14 million Brazilians living in densely populated favelas where basic sanitation is frequently lacking, informal workers are struggling from lost income during lockdown, and social isolation is challenging or impossible. The first case has already been reported in an Amazon indigenous community.

The number of critically ill patients I see, and that people I know tell me about, does not match the number disclosed Dr Isabella Rêllo

Bolsonaro called the pandemic a “little flu” and insisted Brazilians would be immune because they were used to jumping in sewage. His government has distributed just 54,000 tests for a population of about 210 million. Last month the health ministry stopped releasing the numbers of suspected cases.

“In Brazil that’s certainly a critical issue, if not a crisis,” said Albert Ko, department chair and professor of epidemiology at the Yale School of Medicine, noting that widespread testing helped Taiwan, South Korea and Germany blunt the epidemic’s rise.

“It is clear we have to improve the issue of tests, and improve a lot,” health minister Luiz Mandetta told reporters this week.

Street cleaners at work in the city of Niterói in south-east Brazil. Photograph: Nicoló Lanfranchi/The Guardian

Estimates vary wildly. This week, Edmar Santos, health secretary for Rio de Janeiro, said the state could have 50 to 100 infected people for each of its 1,074 confirmed cases.

Brazil’s official toll of 359 deaths is just “the tip of the iceberg,” said Fernando Bozza, a researcher in infectious diseases at the government research institute Fiocruz who is modelling the pandemic. “You have a mountain of other deaths that are either directly or indirectly associated with the epidemic and they are not notified.”

Rêllo, who works in private and public hospitals in Rio, said test results can take up to seven days to arrive. She dealt with three deaths last week alone but results confirming coronavirus arrived after the patients had died – meaning they did not enter the count. The notification systems she deals with vary from handwritten forms to online ones.

“I’m just one doctor,” she said. “The number I am seeing of critically ill patients, of what I see and what people I know tell me about, does not match the number being disclosed.”

She and other doctors are worried about running short of personal protection equipment before the full force of the pandemic has hit.

“It’s chaotic, many cases arriving,” said Rodolfo Espinoza, a doctor working in Rio’s intensive care wards. “We know there are many suspected cases with no diagnosis.”

In São Paulo state, Brazil’s most populous with 44 million people and 4,048 cases, the government laboratory handling tests has a backlog of 16,000, state health secretary José Germann said on Wednesday.

A supermarket in Lapa, Rio de Janeiro, where coronavirus cases could be 50 to 100 times higher than those so far confirmed. Photograph: Nicoló Lanfranchi/The Guardian

At the Emílio Ribas public hospital in the state capital, tests are taking up to 15 days to come back, said Ana Ribeiro, its epidemiological service coordinator. The hospital – one of Brazil’s most respected infectious disease institutions – is currently waiting for 134 test results, including those of three who have died.

“There are many people getting symptoms and they cannot handle it,” Ribeiro said.

Cemeteries in São Paulo are burying 30 to 40 people a day with coronavirus symptoms but, in most cases, no test result, the Folha de S Paulo newspaper reported.

If diagnosis does not improve, there will be a lot of underreporting in the favelas of Rio. This is extremely worrying Rodrigo Brindeiro, molecular biologist

The non-profit group Viva Rio runs six health centres, called UPAs, in Rio de Janeiro, all near favelas and all almost exclusively dealing with respiratory cases.

“People are not going to UPAS for other reasons,” said general coordinator José Pacheco. “I just select the most vulnerable or most serious to test; the vast majority are not tested.”

São Gonçalo, the second biggest city in Rio state, has 10 confirmed cases. Resident Fabíola Lima, a financial specialist, believes there are many more.

She lives with her three sisters, all of whom went to private hospitals after suffering classic coronavirus symptoms like fever, headaches and dry coughs. They were told tests were not available, and sent home. They too were not included in the official tally.

“This number being released is totally unreal. This makes people think everything’s normal,” Lima said, while her sister Christiane, coughed incessantly in the background.

A man walks next to a poster in Rio Centro that reads: ‘Bankers, respect the lives of workers and customers – coronvirus kills.’ Photograph: Nicoló Lanfranchi/The Guardian

Despite outbreaks of Zika, dengue, chikungunya and yellow fever in recent years, the past three Brazilian governments slashed funding for science and technology, said Rodrigo Brindeiro, a molecular biologist at the Federal University of Rio de Janeiro who helped design the test Fiocruz uses.

Brazil is now competing in international markets to buy the test ingredients it needs.

“Our failure was long-term,” he said. “We know that if the diagnosis does not improve rapidly there will be a lot of underreporting in these favelas of Rio and this is extremely worrying.”

In an email, the health ministry said 40,000 more molecular tests were being delivered this week and another 15 million “are being acquired”. It has taken delivery of half a million antibody tests donated by mining giant Vale, which is expected to deliver millions more. Mandetta said the antibody tests have “various degrees of sensitivity”. Health ministry documents sent to states and towns said the tests were probably just 25% accurate in diagnosing negative cases.

These antibody tests will only spot people carrying coronavirus four to seven days after they become infected, said Brindeiro.

Empty streets in Rio Centro. Photograph: Nicoló Lanfranchi/The Guardian

As Brazilians chafed under lockdown and largely ignored Bolsonaro’s demands to get back to work, there are signs that many people also sought reliable information instead of his anti-science, anti-media, populist posturing. Brazil’s biggest newspaper, the Folha de S Paulo – which Bolsonaro has described as “garbage” – reported a record 70 million readers in March.

An interview with biologist Atila Iamarino Iamarino on the TV show Roda Viva this week drew its biggest audience since Bolsanaro himself appeared in 2018, and has been viewed 3 million times on YouTube.

Concerns over the lack of testing were voiced.

“You have the tests, which are the flashlight you can point in any direction and know what’s happening there,” said Iamarino. “Without this flashlight, what you can use is a candle.”