With the first cases detected in September, earthquake devastation risks new stresses, particularly in rebel-held areas.

Aid groups and public health experts warn that a series of devastating earthquakes could exacerbate a cholera outbreak in Syria first detected last year.

The warnings come as rescue operations ceased in both opposition and government-held portions of Syria – and hope diminished amid remaining searches in Turkey – six days after a series of quakes hit the region. Sunday, the death toll topped 35,000 in the two countries, with at least 4,500 dead in Syria.

Across war-torn Syria, where the UN has estimated that 5.3 million people have been left homeless by the disaster, “there was a perfect storm brewing before the earthquake – of increasing food insecurity, collapsing healthcare systems, the lack of access to safe water and poor sanitation”, said Eva Hines, chief of communications for the United Nations Children’s Fund (UNICEF) in the Syrian capital, Damascus.

“More than half of people in Syria depend on unsafe alternative water sources when it comes to their water needs. And that, of course, increases vulnerability to fast-spreading waterborne diseases such as cholera,” Hines told Al Jazeera.

In September last year, the Syrian government declared an outbreak of cholera – a diarrhoeal infection caused by ingesting food or water contaminated by the Vibrio cholera bacteria. The disease can prove deadly, particularly for children.

The outbreak was largely attributed to the country’s war-ravaged water infrastructure, which forced residents to drink and irrigate fields with contaminated water from the Euphrates river in the country’s northeast.

The disease quickly took hold of largely opposition-held swaths of northwest Syria, where at least 1.7 million people displaced by the country’s decade-long civil war live in crowded camps, and about four million were reliant on humanitarian aid prior to the disaster.

As of January 18, nearly half of the suspected 77,500 cases of cholera in the country were in the northwest region, according to the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), with 18 percent detected in camps for the internally displaced.

Meanwhile, more than 2.1 million people in northwest Syria live in “the most at-risk subdistricts for developing a cholera outbreak”, according to OCHA.