Eric Toner, MD, July 3, 2014
On June 27, 2014, the California Department of Public Health (CDPH) reported on an ongoing epidemic of pertussis. A total of 1,100 new cases have been reported in the 2 weeks ending June 24, 2014, bringing the total for 2014 to 4,558. This is almost twice the number of cases in 2013 (2,532). Three infants have died of the disease this year in California.1
Of the 4,558 cases this year, 3,614 (84%) have been in children, with the majority (2,554, 71%) in the 7- to 16-year age range; 142 cases have required hospitalization (0.02%), and 28 (20%) required intensive care. The majority (63%) of the patients who were hospitalized were infants younger than 4 months of age. Of the pediatric cases for which vaccination histories were available, 9% had never been vaccinated against pertussis. Furthermore, of the infants whose mothers' vaccination histories were available, only 16% of the mothers had received the recommended Tdap vaccine during pregnancy.2
The CDPH report notes that pertussis is a cyclical disease that peaks every 3 to 5 years; the last peak was 4 years ago. However, there has been a general increase in the incidence of pertussis over the past 2 decades. In addition to failure to vaccinate, some of this increase is attributed to use of newer acellular vaccines that cause fewer adverse reactions but do not provide long-lasting immunity.
There has also been an epidemic of measles. In 2000, measles was declared eliminated in the US—meaning there was no longer sustained domestic transmission and only rare imported cases. So far this year, there have been 539 cases of measles in the US in 20 states, comprising 17 distinct outbreaks—by far the largest number since 2000.3 In all of 2013, there were fewer than 200 cases in the US, and the median annual number of cases in the US from 2001 to 2012 was 60.4 According to the CDC, the majority of measles patients had not been vaccinated. In cases in which patients had been vaccinated, it is thought that immunity from vaccination waned over time, and with little exposure to the circulating virus there is limited opportunity for natural immune boosting from repeated exposure. Furthermore, many cases are related to an ongoing large epidemic in the Philippines.
This year (as of June 13) there have been 796 cases of mumps in the US. This compares to 438 cases in all of 2013. Most of these cases are related to 2 large college outbreaks.5 In Ohio, there have been 444 cases in 4 counties. Approximately half (243) can be linked to an outbreak at Ohio State University.6 The outbreak at Fordham University was discussed in a previous CBN report.7 The relationship of these outbreaks to vaccination is not clear, since most of the students had been vaccinated.
While our attention has been drawn to large and worrisome epidemics outside the US, such as MERS, H7N9, Ebola, and chikungunya, clinicians in the US should remain aware of the potential for outbreaks in their own communities of what used to be common illnesses. It is worth noting that the pertussis epidemic in California alone involves more cases than the current international epidemics of MERS, Ebola, and H7N9 combined. Importantly, these formerly common childhood diseases are for the most part preventable. In most cases, failure to adequately vaccinate children plays a role in these epidemics. Inadequate vaccination provides fertile ground for epidemics, whether they are sparked by an importation from abroad or by occasional domestic cases.