By Anna Halloran, Epidemiologist, Spokane Regional Health District

A total of 70 confirmed and probable pertussis infections have been investigated by Spokane Regional Health District (SRHD) staff so far this year. Most have been unrelated cases. While only slightly fewer cases were reported during 2018 (65), almost two thirds of last year’s total were related to a large outbreak at a residential boarding school. In 2017, only 32 cases were reported. This year, one adult and two infants have been hospitalized. Vaccination status has varied, though as expected, many cases have occurred in children and adults who have been unimmunized, partially immunized or whose immunization status was unknown.

SRHD staff would like to remind healthcare providers to consider pertussis in their differential when patients present with prolonged cough, regardless of age and even if the patient has been immunized.

• Symptoms usually develop within five to ten days after being exposed, but sometimes symptoms may not be present for as long as three weeks.
• Pertussis has an insidious onset with catarrhal symptoms that are indistinguishable from those of minor respiratory tract infections. The cough, which is initially intermittent, becomes paroxysmal.
• Paroxysms of cough occur more at night and will usually increase in frequency and severity as the illness progresses.
• Immunity provided by vaccinations is thought to wane over time. The illness can be milder in vaccinated individuals and the characteristic whoop may be absent.
• In infants, atypical presentation is common as the cough may be minimal or absent, and apnea or gagging may be the only symptom.

Remember, infants are at risk for severe or fatal pertussis. When you suspect a case in an older child, adolescent, or adult, inquire about contact with infants or pregnant women and consider prophylaxis. Additionally, SRHD usually recommends antibiotic prophylaxis of all household contacts, regardless of vaccination status. This is also true in some instances in childcare settings (particularly if an infectious case has been discovered in an infant classroom). Call SRHD Epidemiology at 509.324.1442 to consult if you are not sure or would like to discuss further.

People with pertussis remain infectious from the start of illness through the third week after the onset of paroxysms or until five days after the start of effective antimicrobial treatment and should be excluded from work or school until five full days of treatment has been completed.

Pertussis vaccines are effective, but not perfect. They typically offer good levels of protection within the first two years after administration, but protection decreases over time. Similarly, natural infection may only protect for a few years. According to the CDC, DTaP vaccines are 80 to 90 percent effective. Among children who get all five doses of DTaP on schedule, effectiveness is very high within the year following the fifth dose; there is a modest decrease in effectiveness in each following year.

James Cherry, MD, MSc, Distinguished Research Professor at the David Geffen School of Medicine at UCLA and one of the nation’s leading researchers on pertussis epidemiology and pertussis vaccine, has published extensively on the topic of waning immunity, in particular, the inferiority of today’s acellular vaccines for pertussis against the whole cell vaccines used up until the 1990s. This inferiority has, in part, contributed to large pertussis epidemics across the country in recent years. In a recent Journal of the Pediatric Infectious Disease Society article, Cherry suggests that we may benefit in the future from the development and use of live vaccines and less-reactogenic whole cell vaccines. He also recommends increasing awareness of pertussis in adults as reservoirs for continued circulation of disease.

With Tdap, CDC estimates seven out of ten people are protected in the first year, and effectiveness decreases in each following year. In spite of the evidence for waning immunity, the Advisory Committee for Immunization Practice (ACIP) currently recommends giving only one dose of Tdap to adolescents and adults who have not previously received the vaccine, with the exception of pregnant women, who should be vaccinated during each pregnancy between 27 and 36 weeks of gestation. It is unknown if ACIP will ever recommend routine Tdap revaccination in the future. After receiving Tdap, people should receive Td every ten years for routine booster immunization against tetanus and diphtheria.