Vaccine-resistant pertussis reported in US

A new vaccine-resistant strain of Bordetella pertussis could be responsible for the increase in whooping cough reported among previously vaccinated children.

Variants of pertactin-negative B pertussis were found in isolates from cases of whooping cough in France, Finland, and Japan. Now researchers from the Centers for Disease Control and Prevention (CDC) have identified the first occurrence of pertactin-negative variants in the United States.

The US researchers analyzed pertactin genes from 12 isolates of B pertussis cultured from specimens obtained from children hospitalized in Philadelphia between 2011 and 2012. After sequencing the entire pertactin coding region, the researchers found that 11 of the 12 isolates were negative for pertactin, a component of the current pertussis vaccine. The mutations had not been previously detected because they were outside the region of the bacterial genome that is normally sequenced.

The pertactin-negative variants of B pertussis could explain the waning immunity of the acellular pertussis vaccine, which replaced whole-cell pertussis vaccine in the 1990s to minimize adverse events associated with whole-cell vaccine.

The researchers say that more information about the new strain is needed before they can make any conclusions whether their finding represents a widespread shift in B pertussis strains. Further laboratory analysis will have to be done with patients diagnosed with whooping cough to determine how common the new strain is in this country.

In 2012 the CDC reported more than 41,000 US cases of whooping cough, including 18 deaths. The highest incidence of pertussis has been among infants aged younger than 3 months.