Tracking the second wave: Your guide to Quebec's latest COVID-19 data

Between September and January, the number of COVID-19 infections rose steadily in Quebec, putting increasing pressure on the health-care system.

The government responded by imposing a growing list of public health rules, first targeted to certain regions and then eventually ordering a province-wide curfew that is scheduled to last until Feb. 8.

Along with the 8 p.m. to 5 a.m. curfew, non-essential stores are closed, as are museums, gyms and restaurant dining rooms.

Office workers have been ordered to work from home, if possible. The manufacturing and construction sectors remain open. 

By Jan. 18, both elementary and high school students had returned to class following a period of online learning earlier in the month.

Here are some charts to help track whether the public health situation is improving, and how it compares with the first wave.

Cases, hospitalizations, deaths: 3 key curves

These are the main figures that the Quebec government has been releasing daily since the start of the pandemic.

Each offers a slightly different perspective of how the epidemic is evolving.

Epidemiologists believe it can take as long as two weeks for symptoms to appear after exposure, so case counts offer a portrait of transmission levels that could be up to two weeks old. Here's a snapshot of where we're at.

In the first wave, the greater Montreal area was the hardest hit part of the province. That's where cases, hospitalizations and deaths were concentrated.

Toward the end of the summer, though, cases began to rise sharply in several outlying regions, such as Chaudière-Appalaches. Quebec City also became a hot spot.

This regional breakdown indicates that during the second wave, infections were distributed throughout the province. 

Hospitalizations and deaths typically occur two to four weeks after the onset of symptoms, so these indicators refer to transmission events that are even older than reported infections.

The hospitalization figures provided by the government are mainly indicators of the provincial health-care system's overall capacity.

At their current level, hospitalizations for COVID-19 are disrupting other hospital services like surgery, endoscopy and medical imaging.

There are 2,164 hospital beds in the province set aside for COVID-19 patients, Heath Minister Christian Dubé said in December.

One additional note when looking at the hospitalizations chart: On May 19 Quebec stopped counting certain COVID-19 patients as hospitalized if they were well enough to be released but still waiting to be transferred to safe institutional care. That caused a sudden artificial decrease in the overall figure.

When looking at deaths, here are two things to keep in mind: Quebec doesn't require a test to declare a death related to COVID-19. It has determined an epidemiological link is sufficient.

Also, the number of deaths announced by the government each day doesn't necessarily refer to deaths over the previous 24 hours. 

The chart below shows COVID-19 deaths on the day they occurred, giving a more accurate picture of past trends.

It underscores how devastating the virus has been for elderly people in care, whether in the long-term care institutions known by their French initials as CHSLDs, or in private seniors' residences for more autonomous people, known by their French initials as RPAs.

Additional numbers for a clearer picture

While the charts above offer a general picture of the current situation in Quebec, there are a handful of other statistics that provide important additional insights.

The positivity rate is a measure of how many tests out of every 100 conducted come back positive. If a higher percentage of results come back positive, it suggests the disease is spreading and there are cases in the community that haven't been detected.

It is also helpful when comparing the first wave to the second wave. While the daily case counts now may surpass first-wave levels, there were more cases going undetected then. The positivity rate is lower now than it was in the spring.

Another thing to consider when looking at this chart: the World Health Organization recommends positivity rates be five per cent or lower for at least 14 days before authorities lift a public-health restriction.  

Public health experts agree that testing is an important tool for keeping COVID-19 outbreaks under control.

Not only does testing make it easier to track the spread of the disease, it results in the isolation of people who are contagious, which helps break chains of transmission.

Since Aug. 1, Quebec has conducted an average of more than 14,000 tests per day.

Quebec's public health institute, the INSPQ, publishes a measurement called the effective reproduction number, or Rt, which tracks the number of other people a single infected person is likely to infect (you can read more about Rt here).

This chart, which tracks the Rt in Quebec over time, can be a helpful tool for visualizing whether the disease's spread is getting better or worse. 

A value higher than one means infections are increasing; lower than one means they're decreasing.