California’s Whooping cough (Pertussis) outbreak – which officials declared as an epidemic last June- has now exceeded that which was seen in the year 2010, with nearly 10,000 cases reported by mid-November.
Almost eliminated in this country by the mid-1970s, Whooping cough has made a worrisome comeback over the past decade (see chart above). The reasons behind these increases are complex, and not entirely understood, but some factors are believed to be:
- lower vaccination uptakes in children and adults
- the move away from whole cell pertussis vaccines to safer (but somewhat less protective) acellular vaccines in the 1990s
- evolutionary changes in the Bordetella pertussis bacteria.
Whooping cough outbreaks are cyclical, and we see localized outbreaks increase every three to five years. The last `big’ year for Whooping cough in California was 2010, but 2014 has turned out to be another very bad year on the west coast. This from the California Department of Public Health.
California is currently experiencing a pertussis epidemic. Pertussis is cyclical and peaks every 3-5 years as the numbers of susceptible persons in the population increases due to waning of immunity following both vaccination and disease. The last epidemic in California occurred in 2010, however, the overall incidence of pertussis has increased since the 1990s.
One reason for the increase is the use of acellular pertussis vaccines, which cause fewer reactions than the whole-cell vaccines that preceded them, but do not protect as long. Young infants are at greatest risk of hospitalization and death from pertussis, therefore pregnant women are encouraged to receive pertussis vaccine (Tdap) during the 3rd trimester of every pregnancy. Pertussis antibodies are transferred from vaccinated mothers to their infants and will help protect them until they are old enough to be vaccinated. The primary DTaP vaccine series is essential for reducing severe disease in young infants and should not be delayed. DTaP can be given to infants at an accelerated schedule with the first dose given as early as 6 weeks of age. Even one dose of DTaP may offer some protection against severe pertussis disease in infants.
9,935 cases with onset in 2014 have been reported to CDPH for a state rate of 26.0 cases per 100,000 population (Table 1).
- Pertussis activity is widespread throughout California (Figure 1).
- Pertussis incidence is higher than was reported in 2010 (Figures 2-3)
- 347 cases have been hospitalized; 80 (23%) of these required intensive care.
Although little appreciated by most Americans today as a serious threat, when my (slightly) older sister was born, whooping cough infected more than a 220,000 Americans each year, and killed about 5,000 of them.
All that began to change in the mid-1940s when the first whole-cell pertussis vaccine - combined with diphtheria and tetanus toxoids (DTP) - was introduced.
It what was such remarkable success, that by the time my daughter was born (in 1977) the number of reported cases had just reached a record-low of 1,010 cases, a decrease of 99%.
But since then, the number of cases has increased dramatically, with 2012 seeing nearly 50,000 cases reported in the United States.
Globally, Pertussis remains a serious public health problem, with the World Health Organization estimating that in 2008 about 16 million people were infected, and roughly 195,000 children died from the disease (cite).
Complicating matters further, last year researchers at St. Christopher’s Hospital for Children in Philadelphia, PA reported that 11 of 12 isolates of B. Pertussis they examined in 2011-2012 using Western blot analysis failed to detect Pertactin (see NEJM: Pertactin Resistant Bordetella Pertussis – United States).
Pertactin (PRN) is a membrane protein that facilitates the attachment of Bordetella pertussis bacteria to epithelial cells in the trachea, and is one of the prime components of the acellular pertussis vaccine introduced in the 1990s.
The researchers state, "To our knowledge, this finding represents the first reported occurrence of pertactin-negative variants of B. pertussis in the U.S.”
Similar pertactin-negative strains have been reported in Japan, France, and Finland. Pertactin-negative strains reportedly remain infectious in humans, and retain lethality in laboratory testing on mice.
While the long-term solution to this problem will have to await the development of newer, longer-lasting, and more broadly protective pertussis vaccines, for now following the CDC’s Pertussis Vaccination Guidelines remains your best strategy to protect yourself and your family.
And for more on Pertussis, visit the CDC’s Pertussis page.