(NEW YORK) — An East Coast heat wave that’s triggered advisories and excessive heat warnings, combined with the U.S.’s ongoing COVID-19 outbreak, could force vulnerable people into making hard choices about their health, experts say.

This week’s heat index, which refers to how hot it feels outside, is expected to exceed 100 degrees in cities including New York, Philadelphia and Washington, D.C.

In response to a heat index expected to reach 110 degrees this week, Washington, D.C., Mayor Muriel Bowser activated a heat emergency in effect through July 22 and closed outdoor public COVID-19 testing sites in the District.

“We are in the middle of some very oppressive and hot days,” Bowser said during a Monday news conference.

“The temperatures would be too dangerous for our staff and volunteers at the public testing sites.”

Bowser encouraged D.C. residents to call their medical providers if they need a COVID-19 test or if they feel ill, since many private providers have inside testing facilities.

Cooling centers are open in neighborhoods across the city, with modified rules due to the pandemic, including social distancing. “Anyone entering a cooling center must wear a mask,” Bowser said. “If you do not have a mask, one will be provided to you.”

Extreme weather during a pandemic exacerbates existing inequality

As with other aspects of the pandemic, this month’s overlapping pandemic and heat wave highlight rampant inequality in the United States.

In extreme heat, vulnerable populations, such as older people living alone and homeless individuals who are exposed to the elements, may be especially susceptible to weather. Extremely hot weather increases the risk of health problems like heat exhaustion, heat stroke and dehydration.

Where you live may dictate whether you survive a heat wave. As the Washington Post previously detailed, poor residents are less likely to have air conditioning and more likely to have medical conditions that are aggravated by hot weather.

Cities are hotter than nearby rural areas and heat disparities also exist within cities themselves. In Washington, D.C., 40 percent of low-income residents live in areas with more empty space and fewer trees, which can contribute to higher heat in those neighborhoods, the Washington Post reported.

High heat can have deadly consequences. During a heat wave in Europe in 2003, for example, 70,000 excess deaths were recorded, according to the World Health Organization. Heat waves have been the top cause of fatalities in the U.S. on average over the past three decades, the non-profit Natural Resources Defense Council reports.

According to the WHO, extreme heat can also trigger higher levels of pollen, which can exacerbate conditions like asthma.

For individuals with respiratory problems, heat waves are already dangerous, according to Dr. Leigh Vinocur, a Baltimore-based emergency medicine physician and national spokesperson for the American College of Emergency Physicians.

Since COVID-19’s symptoms can include respiratory problems and trouble breathing, high heat and humidity have the potential to interfere with recovery.

Cooling centers can offer relief for people without air conditioning in their homes or who are homeless, but also present the potential for disease spread in an indoor space with unrelated people crowding together.

The heat wave complicates the COVID-19 best practices that public health authorities have articulated to the public, including the notion that it’s safer to be outside than inside, because the virus is harder to transmit outdoors, Vinocur noted. During a heat wave, you’re not safer outside if you are going to die of heat stroke, she added.

The mid-Atlantic’s high humidity also makes it harder for humans to regulate their own body temperature, according to Vinocur. “You can’t even sweat to cool yourself off. There’s no evaporation of sweat.”

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