(CNN) -- This is all we know for sure: Kari Bowerman, 27, and Cathy Huynh, 26, were backpacking in Vietnam while on break from their jobs teaching English in South Korea. On July 30, the friends were admitted to Khanh Hoa General Hospital in Nha Trang. Both were vomiting, had difficulty breathing and showed signs of severe dehydration. Huynh was eventually released from the hospital. She returned later that night to hear the devastating news -- three hours after being admitted, Bowerman had gone into respiratory failure and died. Two days later, Huynh was dead. What we don't know for sure is what triggered their deaths.
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Kari Bowerman, 27, and Cathy Huynh, 26, died in Vietnam on July 30
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Their symptoms matched others' who have died in Asia: vomiting, low blood pressure, dehydration
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Experts suspect pesticide poisoning from a spray used to combat bed bugs in the region
The cause of death in every case was eerily similar to the one written on @placeholder's death report: "not yet determined."