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Angel Martinez pours ice water on her head in an attempt to stay cool in the scorching heat in Santa Rosa on Sept. 7, 2022. She has been homeless on and off for several years.

Beach-goers flocked to Crissy Field in San Francisco on the afternoon of Saturday, Sept. 3 as temperatures started warming up ahead of the record Northern California heat wave.

A sign reminds construction workers of the danger of excessive heat while they work at the Antioch Desalination Plant in Antioch, Calif. on Thursday, Sept. 1, 2022.

Bay Area hospitals treated dozens of people for heat-related ailments this week, during what may have been the worst hot spell ever in Northern California, but the true public health impact is unknown because there are few coordinated efforts to track illnesses and injuries caused by weather events, health experts said.

As temperatures soared into the triple digits across the region, hospitals and other emergency care providers reported a spike in people seeking care for conditions including heat exhaustion, heat stroke and dehydration. As of Friday, no Bay Area counties had recorded any deaths directly due to heat, though health officials said those reports tend to lag a few days.

The weeklong heat wave was expected to subside this weekend.

But unlike with COVID-19 and other reportable health conditions, heat-related ailments aren’t routinely tracked by counties or the state. Even for hospitals and other providers that report cases of illness or injury caused by weather, officials said they’re almost certainly undercounted.

This week’s scorching conditions, many health officials say, underscore the urgent need to improve surveillance of the effect of extreme heat on public health as climate change drives up temperatures and leads to longer and more frequent stretches of hot weather. That surveillance, officials say, is critical in order to anticipate the burden on hospitals and other providers and shift resources to communities most affected by hot weather.

And as severe weather events become more common, the need for better information will become even more essential.

“The health harms of climate change-related weather — whether it’s cold or hot — don’t get documented the way” COVID and other diseases are, said Dr. Matt Willis, the Marin County health officer. “What it boils down to is that we probably are underestimating the impact. If we want to really wrap our arms around the true burden, we need to measure it.”

Extremely hot weather can lead to a variety of health problems, most directly heat exhaustion and heatstroke, the latter of which can be fatal. It can also cause dehydration, severe sunburns, fainting and altered mental states, and it can worsen chronic conditions, especially kidney and heart diseases. Bay Area hospitals reported treating patients for all of those conditions this week.

“The body has ways to compensate with exposure to extreme environments, including heat,” said Dr. Kevin Rolnick, an emergency medicine resident who works out of UCSF and San Francisco General Hospital. “But that puts a lot of stress on the body, and it’s not something the body can undergo for extended periods of time without ill effect.”

It’s challenging to track heat-related ailments because symptoms — such as fatigue, dizziness and nausea — often are fairly broad and could apply to many conditions. Also, health care providers aren’t required to report heat exposures.

If patients come to the emergency room because they fainted, they’re dehydrated or they are confused or otherwise mentally altered, their cases may not be recorded as heat related even if that’s the obvious cause, health experts said. The same applies to tracking 911 calls.

“There is always a surge in call volume when there is a heat wave,” said Neetu Balram, a spokesperson for Alameda County Public Health Department. But even when calls are clearly heat-related, “they are rarely coded or categorized as such. They are usually categorized based on symptom rather than causation.”

With spotty surveillance, it’s impossible to say, for instance, whether this record heat wave affected public health more gravely than earlier events. But across the region, health officials said there were generally fewer people requiring medical treatment than they had expected, even in places where temperatures were well over 100.

Only a handful of patients had symptoms serious enough to require hospitalization, according to informal reports from counties and health providers.

At John Muir Medical Center in Contra Costa County — among the hottest places in the Bay Area this week — 13 people were treated in the emergency room for heat exhaustion or heatstroke, and 41 others were seen for dehydration due to heat exposure as of Thursday, a spokesperson said. One person was hospitalized for hyperthermia, where the body temperature is over 107 degrees.

“I had the general sense that we didn’t see a big impact, which is really good news, if in fact that’s true. I expected them to be quite a bit higher,” said Dr. Daniel Peddycord, chief climate and health policy officer for Contra Costa County, who agreed with Willis that heat-related cases may have been under-reported. “We had seven, eight, nine days — that’s a long heat stretch. Probably one of the reasons we managed to squeak through was it did cool off in the evenings pretty well, most of those days.”

In Sonoma County, where temperatures also climbed well over 100 for most of the week, officials at Santa Rosa Memorial Hospital said there was a notable increase in people seen for heat-related conditions, though they didn’t have exact numbers. Dr. Omar Ferrari, chief of emergency medicine, said there were fewer patients than he’d anticipated, but added that more people came in later in the week, even as temperatures cooled a bit, suggesting that the duration of the extreme weather was a factor.

“The predominance of the folks coming in has been just recently,” Ferrari said on Friday. “Nothing really dramatic, but as this has gone for a prolonged period of time, I think people are succumbing. There’s no respite.”

Willis said he was aware of three people hospitalized in Marin County with heat-related issues, though he suspects more patients may have been admitted for conditions indirectly tied to the hot weather — worsening heart or respiratory problems, for example.

Of the three hospitalizations directly tied to heat, one was an older person with early dementia who lives alone and who wandered onto a porch, where the person stayed outside for too long and ended up with hyperthermia, dehydration and a bad sunburn. A second person was found intoxicated and unconscious on the street and later diagnosed with heatstroke. The third individual was home when the air conditioning stopped working; as the indoor temperature slowly climbed, the person became dehydrated and developed symptoms of severe heat exhaustion.

All of the individuals have since fully recovered, Willis said.

“Those are the most extreme scenarios,” he said. “There are presumably others where it was less acute.”

Erin Allday is a San Francisco Chronicle staff writer. Email: eallday@sfchronicle.com Twitter: @erinallday

Erin Allday is a health reporter who writes about infectious diseases, stem cells, neuroscience and consumer health topics like fitness and nutrition. She's been on the health beat since 2006 (minus a nine-month stint covering Mayor Gavin Newsom). Before joining The Chronicle, Erin worked at newspapers all over the Bay Area and covered a little of everything, including business and technology, city government, and education. She was part of a reporting team that won a Polk Award for regional reporting in 2005, for a series of stories on outsourcing jobs from Santa Rosa to Penang, Malaysia. Erin started her journalism career at the Daily Californian student newspaper and many years later still calls Berkeley her home.