California health officials are laying the blame for the state’s lethal 2010 outbreak of pertussis — also known as whooping cough — squarely at the feet of parents who refused to vaccinate their children as part of a bogus autism scare. According to NBC News, the outbreak, which killed 10 infants and sickened more than 9,000 others, was the worst the state has seen in 60 years.

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A study released Monday in the medical journal Pediatrics analyzed the outbreak pattern and tracked the number of children whose parents filed for “non-medical exemptions” from the state’s vaccination program. Non-medical exemptions are given to families whose children are well enough to tolerate the vaccine, but who refuse to administer it to them anyway for religious or other reasons.

The California Department of Health identified 39 statistically significant geographic clusters of families seeking non-medical exemptions and two major zones of whooping cough cases. According to the data, non-medical exemption families were 2.5 times more likely to also live in an outbreak zone.

According to the study abstract, “The association remained significant after adjustment for demographic factors. Non-medical exemptions clustered spatially and were associated with clusters of pertussis cases.”

Historically, pertussis was a leading cause of infant mortality, killing thousands of children each year in the U.S. alone before the invention and implementation of vaccine programs. A bacterial infection caused by the microorganism Bordetella pertussis, whooping cough got its colloquial name from the high-pitched “whoop” sound infants make as they gasp for breath between violent bouts of coughing.

Pertussis is particularly deadly to newborns, in whom the constant coughing can cause pneumonia, brain injury, failure to thrive and death. The disease organism possesses an ability to suppress the body’s immune response, allowing it to rampage through the body unchecked. Children and adults with pre-existing immunological issues are more vulnerable to the disease than individuals with functional immune systems.

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Families refuse to vaccinate their children for various reasons, but in 1998, British physician Andrew Wakefield published a now-roundly discredited study linking the Measles Mumps Rubella vaccine (MMR) with the onset of autism. Wakefield’s fraudulent research caused him to be banned from practicing medicine in the U.K. after being found guilty of “serious professional misconduct.”

Wakefield now practices medicine in Austin, Texas and has embarked on a campaign to sue his critics for destroying his professional reputation. Many of the cases he has filed in the U.S. are continuations of cases that were dismissed as groundless by U.K. courts.

The last time the state of California saw so many pertussis infections and deaths was 1947. Health officials and physicians pointed to a number of possible factors for the 2010 outbreak, including waning efficacy of the strain of Bordatella pertussis currently used in vaccines, improved diagnostic accuracy leading to the discovery of cases that previously went undetected and the cyclical nature of pertussis outbreaks, which tend to peak every two to five years.

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After analyzing the geographical overlap, however, of pertussis cases and parents requesting exemptions from the vaccination program, researchers concluded that refusal to vaccinate was definitely a major factor in the 2010 outbreak and resultant deaths.

[image of baby in oxygen mask via Shutterstock.com]