The hospital became Mexico's first hot spot for the coronavirus-caused disease COVID-19.
At least four of the infected workers are currently hospitalized as a result of the outbreak, which has given rise to concerns that the underfunded healthcare system in Mexico is unwilling to cope with a major epidemic in the nation of nearly 130 million.
At the start of the outbreak, managers "said no need for protective equipment," said nurse Charly Escobedo Gonzalez who works at the Monclova hospital.
Answering Reuters' questions about the reports that hospital management told staff not to wear masks, a senior official at Mexico's main IMSS public health service that runs the hospital said the health workers should be believed, but he did not confirm the report details.
"Specifically, if they say that we have to believe it, of course," said Raul Pena Viveros, official of the IMSS. He said there may be misunderstandings about where wearing protective equipment is appropriate inside a hospital.
"Not all the workers inside the hospital must wear the same equipment. And when this kind of equipment is badly used ... it runs out faster and they put workers at risk who are in contact with patients, "he said.
Mexico registered 4,661 people with coronavirus and 296 deaths, a fraction of the figures in neighboring USA, but the coronavirus arrived in the Latin American country weeks later.
In the third week of March the Monclova hospital became a focal point for coronavirus, highlighting a lack of masks and even soap and bleach there, staff said.
As staff started falling ill, hospital floor managers instructed healthcare workers not to use facemasks that some had bought for themselves because of lack of hospital equipment, seven workers told Reuters.
Pena Viveros said in March the hospital had been short of protective equipment and other materials for fighting coronavirus.
Health officials have not given a detailed explanation of why so many healthcare workers in Monclova have become infected.
Hospital workers are at higher risk of contracting the coronavirus unless they wear protective equipment such as facemasks and gloves. The N95 respiratory masks provide more protection from other infected people whilst simpler surgical masks help the wearer avoid spreading the virus.
Pena Viveros said due to a lack of proper N95 masks, some hospital staff were also wearing inappropriate industrial-style masks that were donated to them, too.
Later the lack of N95 masks was resolved, said Pena Viveros, who was sent from Mexico City by IMSS head to investigate the Monclova hospital and spent a week there early in April. Staff say the hospital now has more protective equipment but still lacks equipment like masks.
Three nursing staff said that while some colleagues chose not to wear facemasks after being told that they were not necessary by managers or supervisors, they continued to be worn by other personnel.
On the night of March 22, one of the nursing staff's heads told a group of doctors and nurses gathered in the emergency room to take off their N95 masks because, according to a nurse who heard the order, they were not required.
Another nurse, surnamed Hernandez Perez, received a similar order a few days earlier from a deputy head of nursing.
"The subhead told us in a morning clinical class not to create panic ... that we shouldn't wear facemasks because we'd be creating a psychosis," said Hernandez Perez, who didn't want to use her full name. She is now sick at home and has tested positive for the coronavirus-caused respiratory disease COVID-19. A second nurse confirmed the account of Hernández Pérez.
Reuters could not speak to two of the nursing managers at that meeting who nurses say spoke.
In early April, after media accusations that the Monclova hospital was badly lacking equipment to deal with the virus, IMSS head Zoe Robledo announced that the hospital's director had been temporarily replaced.
Neither Ulises Mendoza, the suspended hospital manager, nor the current hospital director responded to repeated requests from Reuters for comment.
One nurse, who asked not to use her name for fear of retaliation, said that superiors repeatedly told her not to wear a facemask while working in high-risk areas such as the hospital's ground floor, where the emergency room is located, during the second half of March. As well as the 51 confirmed cases, Pena Viveros said that more than 300 other workers have been sent home temporarily as the hospital scrambled to contain the outbreak.
He said the hospital had contracted nurses and doctors from other services to resolve the shortage of staff, yet the ability of the hospital to care for patients was impeded, some staff said.