In the worst COVID-19 outbreak so far in Maine, the virus swept quickly through Cape Memory Care, a home for patients with dementia and Alzheimer’s, infecting 61 patients and 23 staff members. Six residents of the center in Cape Elizabeth have died.

But while the events at Cape Memory Care were tragic, the story of what unfolded there is also one of prevention.

Of what didn’t happen.

The first case was discovered during the week of May 20, the week the Maine Center for Disease Control and Prevention expanded its testing capacity under a state partnership with Idexx, which makes COVID-19 tests. As a result of the expansion, the Maine CDC no longer waited for three cases to occur in a congregate care setting before ordering tests of all residents and staff. Instead, they tested everyone at Cape Memory Care immediately.

The rapid, widespread testing enabled the state to quickly identify infected staff – more than half of whom had no symptoms of COVID-19 – before they could spread the highly contagious, fast-moving virus to others in the community. Maine CDC workers halted potentially exponential spread to dozens or even hundreds of other people with detection and quarantining of those who were contagious.

“We absolutely dodged a bullet. We dodged a lot of bullets, actually,” said Dr. Meghan May, professor of microbiology and infectious disease at the University of New England.

The Cape Memory Care outbreak illustrates the vital importance of rapid testing and tracing to contain the virus. Done on a large-enough scale and combined with physical distancing measures, the strategy can drive down case numbers, health experts say.

Testing supplies had been restricted in Maine before the state’s agreement with Idexx, in part because of a national shortage of supplies and testing equipment, one of the Trump administration’s failures to contend for the pandemic. Those shortages have since eased, starting in May.

In July, testing will again surge with a further deepening of the partnership with Idexx and the creation of a mobile lab. Maine’s testing capabilities in July – at about 35,000 tests or more per week – will be more than seven times what they were in early May. Mainers in higher-risk categories will be able to get a test without a doctor’s note.

Dr. Nirav Shah, director of the Maine CDC, said with further testing expansion, the agency is strongly considering routine surveillance testing of residents and staff at congregate care facilities before any cases emerge.

For Cape Memory Care, the expanded testing and tracing program meant a head start of days if not weeks in clamping down on the spread of the virus, a crucial period for preventing community spread. The 23 infected staff members and their close contacts were quarantined for 14 days starting in mid-May. Because congregate care facilities have not been accepting visitors since March, residents who contracted COVID-19 could not pass it on to family or friends.

But staff members going home and out in the community could spread the disease.

“Even one day, two days can make a big difference,” said Jennifer Kates, senior vice president and director of global health and HIV policy at the Kaiser Family Foundation, a national health policy institute. “The more testing, tracing and isolating you are doing, the more you are preventing the next spread of the virus.”

More than half of the 23 infected staff members – and perhaps more – were asymptomatic at the time they received a COVID-19 test, according to the Maine CDC and Cape Memory Care officials.

Matthew Walters, Cape Memory Care’s managing director, said wide-scale testing of residents and staff, and the ability to retest periodically, is critical for congregate living facilities.

“We insisted on testing all residents and all staff after learning of a single positive staff member,” Walters said in a written statement. “The testing was conducted in less than 24 hours. This rapid universal testing of over 100 individuals allowed us to learn the scale of the outbreak and to initiate interventions without delay.”

Exponential growth

It’s difficult to estimate how many cases were prevented because much is still unknown about the virus, said May, the UNE professor. The virus grows exponentially, but how widely it spreads from one outbreak depends on a number of factors, such as how much physical distancing is occurring in the overall population and among the people who are infected.

Shah, the Maine CDC director, said the agency does not know how many cases from the Cape Memory Care outbreak were prevented in the community,

“The qualitative answer is ‘a lot,'” Shah said. “I don’t know the answer. It’s a great question. We know the answer is a fair number.”

Shah said discovering cases in people without symptoms or before they develop symptoms helps to prevent community spread. That’s because COVID-19, unlike the flu, can easily spread before people develop symptoms. The flu is contagious, but people tend to feel ill and stay home at the same time that they are most likely to transmit the virus, Shah said, limiting its spread. The flu also has an annual vaccine, while there is not yet a vaccine for COVID-19.

With COVID-19, people are most contagious in the day or two before they have symptoms, or on the first day they have mild symptoms but don’t realize they have the virus.

“That’s what makes this virus completely different from almost any other infectious disease,” Shah said.

Common COVID-19 symptoms include a dry cough, shortness of breath and a fever.

Maine CDC’s testing expansion means that they are undoubtedly finding more cases in people who are pre-symptomatic or asymptomatic, Shah said.

Another complicating factor is that certain people for unknown reasons are “super spreaders.” Research conducted on case studies – such as a choir practice in Washington state – traced dozens of COVID-19 positive cases to a single person.

The R factor

Scientists estimate the exponential spread of a virus by R (0 or naught) and R (e or effective). R (0) is the reproduction rate of the virus if it is left unfettered in the population, with no control measures in place and before people have developed immunity. The R (e) rate is after some control measures have been put in place, such as physical distancing, and also after some in the population recovered from the virus and are now immune.

If the R rate goes below zero, that means the virus is fizzling out. But an R rate even slightly above 1 can result in exponential growth.

The current R (e) rate in Maine is slightly below 1, according to the Maine CDC, but because of the state’s low population and the exponential growth of the virus, the R (e) rate can change quickly if there are spikes in cases.

There have been many estimates of what the R (0) rate – the rate when no measures are taken to halt its spread and before people have developed immunity – is for the novel coronavirus, but some scientists peg it at between 2 and 3.

At Cape Memory Care, for example, if asymptomatic people unknowingly spread it to relatives and friends at an R (e) rate of 1.05, which was the statewide average in mid-May, it could have caused an additional 49 cases two reproductive generations removed from the original infections. At an R(e) of 1.25 – slightly worse than the statewide average at the time – the 23 cases could have caused an additional 65 cases two reproductive generations removed. At an R (e) of 2.5 – more of a worst-case scenario – an additional 201 cases could occur two generations removed.

“R is a very difficult measurement to pin down. There are so many unknowns,” May said.

What is known is that testing, tracing and isolating works. If everyone is tested and isolates properly, it may not spread to anyone else.

“These are tried and true public health measures, but they need to be done on a massive enough scale. You need to always be a step ahead of the virus,” said Kates, at the Kaiser Foundation.

According to research published in the United Kingdom by the Royal Society DELVE initiative, a quick and effective testing and tracing program can halt the progress of the virus. The analysis showed a response time that was two days faster – from five to three days – led to a 60 percent reduction in R(e).

Dr. Michael Mina, assistant professor of epidemiology at Harvard T. H. Chan School of Public Health, said that the “tracing” part of testing and tracing is key, because if you test but don’t trace contacts, the virus can still spread.

“The most effective contact tracing happens when case counts are low,” Mina said. Maine is also expanding its contact tracing capabilities in concert with increased testing.

Maine’s case counts have declined in recent weeks after the Cape Memory Care outbreak and other outbreaks subsided. The seven-day average of daily new cases in Maine has dropped from 52.6 in late May to 30.4 on Monday.

Percent positive

One of the key metrics for determining the effectiveness of the testing, tracing and isolation strategy is the percent positive rate.

Maine’s positive COVID-19 rate of all tests given has trended lower as testing has expanded, and was down to 4.46 percent by Tuesday after being between 5 and 6 percent for much of the pandemic. After testing expanded in mid-May, the daily percent positive rate has usually been about 2 to 3 percent, which is slowly reducing the cumulative rate.

When the positive rate trends lower, that means the public health agency is finding most cases of the virus and finding more asymptomatic cases, Shah said, which reduces transmission.

The goal of the Maine CDC is to drive down the cumulative percent positive rate to between 2 and 3 percent or lower, which is similar to what South Korea has done.

South Korea implemented an aggressive testing and tracing strategy at the beginning of the pandemic and has controlled the virus and avoided large-scale deaths. South Korea has five deaths per 1 million population compared to 359 deaths per 1 million in the United States. Maine has had 75 deaths per 1 million population.

Many states have started reopening to a greater extent than Maine even though they don’t have a comprehensive testing and tracing program. Some states, including California, Georgia, Tennessee, North Carolina and Texas, are starting to see spikes in cases and hospitalizations.

May said “Maine is one of the best positioned out of almost any of the states.” Hospitalizations have also declined in recent weeks, but tourist season poses a major threat, as well as protests where large numbers of people congregate. Maine is also continuing to gradually reopen, and has relaxed some restrictions on tourism.

Kates said while testing, tracing and isolating works, it doesn’t mean that all physical distancing measures can stop without risking a major resurgence of the virus.

“Until we have a vaccine, there will always be a need to have some physical distancing in place,” Kates said.

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