Maria Teresa Quiej Alvarez, one of two conjoined twins separated earlier this month at Mattel Children’s Hospital at UCLA, is in serious condition with stable vital signs following a three-hour surgical procedure performed Friday, Aug. 16, after tests overnight showed a bacterial infection in the lining of her brain.

Led by Dr. Jorge Lazareff, the hospital’s director of pediatric neurosurgery, a medical team drained blood from her brain that could be aiding the infection’s growth. The blood was remaining from a subdural hematoma, or build-up of blood in the brain, that occurred during the separation surgery.

Her sister, Maria de Jesus, remains listed in serious condition with stable vital signs in the hospital’s Pediatric Intensive Care Unit (PICU). Maria de Jesus now is feeding from a baby bottle and eating standard baby food. Her breathing tube was removed on Aug. 13, and she continues to breathe on her own.

The twins, who were conjoined at the head, were separated Aug. 6 in a nearly 23-hour surgery. Maria Teresa underwent a two-part, five-hour surgical procedure later that day to address the subdural hematoma. The condition of both girls was upgraded from critical to serious earlier this week as ventilators were removed and they began breathing on their own.

Both have grown progressively more alert and active in the days following the separation surgery. Doctors remain cautiously optimistic about the long-term prospects for the recovery of both girls.