Mexico's first death confirmed to have be caused by H1N1 flu demonstrates why the virus has been so difficult to contain.

39-year-old Maria Adela Gutierrez was a mother of three and worked as a door-to-door tax inspector in Veracruz State. Pig farming is a key industry in the mountain hamlets in Veracruz, where small clinics provide the only local health care.

Gutierrez went to hospital gasping for air, with her hands and feet blue from oxygen-starved blood. Doctors treated her but could not identify what was wrong with her, and her condition worsened.

On her third day in the intensive care unit, the test results indicated coronavirus - a highly contagious disease associated with severe acute respiratory syndrome, or SARS. Gutierrez died just before a second round of tests came back negative for coronavirus. Her condition has since been identified as H1N1 flu.

Two other patients died of pneumonia in the Oaxaca hospital, showing no atypical symptoms.

Dr. Jesus Manuel Salcedo, Oaxaca Hospital, said, "Her evolution from day 9 to day 10, and the lab tests that were done, showed that it was not a typical case, as with other pneumonias contracted in the area.

She presented altered liver enzyme function and low leukocytes, which implies a different type of problem."

(CCTV.com May 1, 2009)