Hospitals brace for a surge of coronavirus patients, but how accurate are the projections?

A Boston EMS ambulance crew wheeled in a patient to Massachusetts General Hospital from their ambulance on Wednesday.John Tlumacki/Globe Staff

At some point over the next two weeks, hospitals across Massachusetts are expected to confront a significant surge in the number of coronavirus patients, putting their capacity under enormous strain and potentially claiming thousands of lives.

The bleak projections about the coming wave, however, vary significantly. Some of that uncertainty is due to limited testing across the state, and the unknown extent of the population that has been infected. There’s also the question of how effective social distancing has been in curbing the virus’s spread.

At a news conference this week, Governor Charlie Baker said the expected surge could come as early as Friday, citing infectious disease models that seek to predict the contagion’s trajectory despite limited and rapidly changing information.

“I don’t know exactly what the slope of this line ultimately looks like or how far out it goes,” Baker said. “But based on all the modeling our folks have done, by April 10, we need to be in a position to presume we’re going to see a fairly significant increase in hospitalizations.”

At a news conference on Wednesday, he added, “We’re continually reviewing the modeling, but right now we see evidence that we’re still on the upward slope of this pandemic.”

A Cataldo ambulance drove away from Massachusetts General Hospital. Jessica Rinaldi/Globe Staff

Officials at the state Department of Public Health have based their models on the experience of Wuhan, China, the initial epicenter of the coronavirus, where there was an average of an eight-day delay from the onset of symptoms to an admission to a hospital.

“The main takeaway is that in Wuhan, very effective social distancing measures [delayed] the cases per day by onset of symptoms within a week, but cases diagnosed, hospitalizations, and the corresponding bed-surge peak were not seen for two weeks or more after social distancing went into effect,” said Ann Scales, a spokeswoman for the department.

A month ago, Massachusetts had just eight confirmed cases and no known deaths. On March 24, a stay-at-home advisory took effect, shutting down large swaths of the economy. By Wednesday, with 87,511 people tested, the state reported 16,790 positive cases for the virus, 433 of whom had died.

Asked how state officials would know when cases were peaking, Scales said “the virus will dictate the timeline.”

Sample HTML block

“We will know that we are approaching a peak when the number of confirmed cases per day and the number of cases hospitalized plateau,” she said. “We are monitoring many indicators daily to evaluate where we are relative to ‘peak,’ and adjusting assumptions as we learn more about COVID hospitalizations, percent of hospitalizations in the ICU, and length of stay information," she said.

But the state’s models could be underestimating the severity of the peak, as well as its duration.

Recently updated models from the University of Washington’s Institute for Health Metrics and Evaluation suggest that the state’s death toll will peak on April 18, when there will be an estimated 213 COVID-19-related deaths, with more than 150 lives lost per day over the following week. A day before, the institute estimated there would be as many as 373 deaths a day at the peak, with more than 300 lives lost per day over the following week.

On the same day, that model suggests the state will need 8,028 hospital beds for COVID-19 patients — 3,180 more than typically exist — and 1,873 intensive care beds, or 1,596 more than typically exist.

By August, if the institute’s model is accurate, nearly 5,625 people in Massachusetts are expected to die from the virus. By contrast, the state model projects a maximum of about 4,300 could die.

Scales declined to comment directly about the institute’s estimates.

“There are hundreds of models out there,” she said. “We are building as much capacity as we can . . . and will continue to do so.”

The state’s models, she added, are based on confirmed cases, not the actual number of people who have been infected. “They are meant to guide us in ensuring that we have capacity available to care for people who get sick,” Scales said. “We’re confident these models are helping us move in the right direction.”

Dr. Paul Biddinger, director of the Center for Disaster Medicine at Massachusetts General Hospital, said he also remains confident in the state’s models.

His hospital has been updating its projections for the surge twice a day, based on data from hospitals across the Mass. General Brigham system.

“It’s not possible to say with certainty, but our models have been showing a slowing of the rate of rise of new cases that we believe reflects the social distancing measures enacted,” he said. “We are cautiously optimistic based on this data that we will not exceed prior projections.”

William Hanage, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health, was also skeptical about the institute’s model.

But for different reasons. The institute’s projections suggest the surge in Massachusetts could be short-lived, as a result of the social distancing measures.

However, Hanage expects the surge will be more of a sustained plateau, rather than a sharp peak, given that the state has allowed far more movement of the population compared to Wuhan or northern Italy, where there was much more of a state-enforced lockdown.

“I don’t buy into this model, because I think it exaggerates how effective social distancing will be at stopping new infections,” Hanage said. “Because we didn’t enact the kind of measures that succeeded in Wuhan, we’ll have a longer period in which our health care system will be under considerable strain.”

Given the expected rush of cases, the state still has much work to do to prepare its hospitals.

When asked if Massachusetts has enough ventilators to help COVID-19 patients breathe, Baker said, “We’re going to need to get more of them.”

At the Beth Israel Lahey Health system, which on Monday reported 545 patients who either tested positive or had symptoms suggesting they had the virus, officials were racing to prepare for the worst.

“We are sorely constrained on the amount of PPEs and ventilators we have,” said Dr. Kevin Tabb, president and chief executive of Beth Israel Lahey Health, referring to personal protection equipment for medical staff. “If I had a magic wand, I’d wish for a lot more than we have now.”

At their 13 hospitals, about 30 percent of COVID-19-positive patients have required treatment in an intensive care unit, with nearly all of them on ventilators, he said.

They’ve already filled all their regularly licensed intensive care beds and converted many others to be able to treat COVID-19 patients with breathing problems and other dangerous symptoms.

Tabb and officials at other local hospitals said they were expecting the surge around the same time as the state models project.

“We remain very concerned but cautiously optimistic,” he said. “We know for a fact that numbers will continue to rise and that the ability of the entire health care system to address this crisis will be tested.”

To prepare, hospitals have been maximizing their capacities, canceling elective procedures, and expanding their abilities to treat patients in need of intensive care.

At the same time, the state is preparing new medical wards at the Boston Convention Center and the DCU Center in Worcester. Officials are also considering opening similar facilities on Cape Cod and in Western Massachusetts, as well as in nursing homes throughout the state.

At Brigham and Women’s Hospital, where Tuesday afternoon there were 132 patients that either tested positive or had symptoms of the virus, the staff has been working seven days a week, with little sleep, to prepare for the coming surge. More than 180 of the staff — or 9 percent of those tested — have been diagnosed with COVID-19.

“We don’t feel overwhelmed yet,” said Dr. Paul Sax, clinical director of the hospital’s division of infectious diseases.

But much of the hospital has been reserved for coronavirus patients, and intensive care beds are filling up.

Sax said he hopes the hospital has enough ventilators and protective equipment for its staff. But that depends on how long the surge lasts, and how bad it ultimately gets, he said.

“There are a lot of unknowns,” he said. “We’ve never seen anything like this before.”