Whooping cough has reached epidemic proportions in Texas with nearly 2,000 cases reported so far this year, including two infants who died, according to health officials.
The children were too young to receive the whooping cough vaccine, state officials said. The overall number of cases likely will surpass the recent high of 3,358 in 2009, according to the state health services department.
"We're clearly having an epidemic," said Dr. Carol Baker, the director of the Center for Vaccine Awareness and Research at Texas Children's Hospital in Houston.
Dr. Lisa Cornelius, Texas infectious diseases medical officer, said: "This is extremely concerning. Pertussis is highly infectious and can cause serious complications, especially in babies, so people should take it seriously."
Pertussis, or whooping cough, is a bacterial infection that often begins with cold-like symptoms and a mild cough, followed a week or two later by severe coughing that can last for several weeks.
It spreads when an infected person breaths, coughs or sneezes. People of all ages can get whooping cough, but infants have the greatest risk of contracting it, they said.
The Texas Department of State Health Services issued an alert this week urging doctors to screen for whooping cough and encouraging residents to get vaccinated.
Last year, 49 states reported an increase in whooping cough cases, but most states have experienced declines so far this year. Researchers attribute the rise to a new type of pertussis vaccine, which is safer but less effective over the long run, and to a decline in the number of children being vaccinated.
Whooping cough vaccinations for infants can't be completed until babies are four months old, Baker said.
Most children are vaccinated by the time they reach adolescence, she added. Vaccination is recommended during pregnancy to protect the mother and the newborn.
Last year, more than 41,000 cases of whooping cough were reported in the United States, according to the Centers for Disease Control and Prevention. Infants had the highest rate, followed by children ages 7 to 10.
In 2012, 49 states and the District of Columbia reported increases in cases compared to the year before, the CDC said. Most had double or triple the rate of prior years.
So far in 2013, only 16 states are ahead of last year's pace for whooping cough, the data showed. More than half are in the South.