What’s All the Whoop About? Resurgence of Pertussis in California

California is in the midst of another infectious disease epidemic. Not a residual H1N1 pandemic influenza threat, but an epidemic caused by Bordetella pertussis — the bacterium that causes whooping cough. Whooping cough’s primary clinical feature is the potential for a severe, lingering cough that can persist in many patients for weeks, if not months.

In the 1920s and 1930s, pertussis was an annual concern as a feared childhood killer. National annual infection rates were as high as 250,000 cases with as many as 9,000 deaths each year. In the 1940s, health authorities introduced a combined vaccine against diphtheria, pertussis, and tetanus (DPT, now replaced with DTap). By 1976, in the United States, as a result of routine DPT vaccinations of children, pertussis in children had been virtually eliminated — there were only 1,010 cases reported that year.

As healthcare professionals we know — and we must keep in mind — that pertussis outbreaks run in cycles. Cases tend to peak every three to five years as vaccine-induced immunity (in the general population) wears off. The last outbreak “peak” in California was in 2005, when 3,182 cases and eight deaths were reported. In 2010 we are running at a pace that suggests that the number of pertussis cases in California will reach a peak that will surpass the maximum observed cases, including deaths, in the past 50 years.

As of Sept. 7, 2010, 3,834 cases have been reported in California, a seven-fold increase from the same period during 2009, when 530 cases were recorded.

Our attention needs to focus first on unimmunized or incompletely immunized infants, a patient category that is particularly vulnerable. The 2010 epidemic has already resulted in the deaths of nine infants younger than three months. Most of these children were too young to have received a pertussis vaccination. Eight of the nine children who died this year were Hispanic. Statistics confirm that pertussis infection rates among infants are typically higher for Hispanics than for any other ethnic group in California.

The clinical symptoms of pertussis can be difficult to distinguish from those of other respiratory infections. Symptoms may appear at first similar to those of a common cold: runny nose or congestion, sneezing, mild cough. Fever is often not present. At three weeks post-infection, 97 percent of patients will have a cough, and in 72 percent the cough will be severe (paroxysms). After more than nine weeks, 52 percent will still have a cough symptom.

Infants and children with the disease cough violently, rapidly, and repeatedly, often with a loud “whooping” (69 percent) sound. Post-tussive emesis occurs in 65 percent. More than half of infants who are less than a year old must be hospitalized, and one in five will also develop pneumonia. About one in 100 will experience convulsions.

Diagnostic testing is of relatively low sensitivity, particularly later in disease. Treatment is often delayed due to late presentation of the patient or late recognition by practitioners. Although treatment is important to reduce spread of infection, it may not influence the clinical course of the disease. Prevention is the best option.

Children receive DTaP vaccine at 2, 4, and 6 months of age, with a booster at 15 to 18 months. An additional booster vaccination is given at age 4 to 6 years, typically linked to entering school. Infants must receive the first three shots in the vaccination series for maximum protection. There is now a vaccine for older children and adults, Tdap, which serves to boost the immunity that wanes after childhood immunization or natural disease. All children beginning at 11 to 12 years and all adults should receive a single dose of Tdap to renew their protection against pertussis.

California’s effectiveness in accomplishing immunization of young children is better than the national average. In 2008, the coverage rate for three or more doses of DTaP among children 19 to 35 months of age was estimated to be almost 98 percent for California, compared to about 96 percent for the nation (CDC survey). California is not as successful (nor is the rest of the nation) at vaccination of children aged 11 and 12 years. In 2009, 53 percent of California children aged 13 to 17 years had received at least one dose of Tdap. Unfortunately, only 6 percent of adults nationally have received their Tdap booster.

California legislation is pending that would require children entering middle school to be vaccinated against pertussis. Boosting California’s immunization rates is also a goal of another proposed piece of legislation that would require health insurers to reimburse physicians for the full cost of purchasing, storing, and administering vaccines. A similar measure, co-sponsored by CAFP, was introduced in 2009 but died “in committee” due to financial reasons.

Who should be vaccinated with Tdap? Since the source of infection for an infant is usually an adult, parents, family members, and caregivers of infants need a booster shot prior to providing care. Thus an ideal location for emphasizing immunizations is in obstetrics clinics and practices so that immunizations can be given during the last two trimesters, or at first follow-up after delivery. Others who are in routine contact with infants, including healthcare and childcare workers, should be vaccinated. The California Department of Public Health (CDPH) issued a new pertussis immunization recommendation with the objective of helping to curb the current pertussis outbreak.

CDPH Recommendation

One dose: Tdap to anyone age 10 and older who is not fully immunized, including adults older than 64. This is especially important for individuals who care for infants and to women of childbearing age, either before they become pregnant, during pregnancy (the second or third trimester), or, failing that, immediately after the child’s birth. CDC recommendations include the substitution of Tdap for Td boosters for patients during an emergency department visit for wound management, unless the patient has already received a Tdap. There is also no need to wait for 5 to 10 years, as was historically traditional. Tdap can be given at any interval following a previous Td. Pertussis incidence waxes and wanes. It is not clear why California is experiencing current epidemic proportions of the illness, and the most deaths in half a century. Numerous factors are suspected:

• Cyclic nature of pertussis — and we are at the peak of a cycle.
• Immunity has lessened in teenagers and also in older adults — protective immunity post vaccination begins to decline in four to 12 years.
• Gaps in vaccination coverage — especially older children and adults.
• Some doctors don’t offer the recommended immunization schedule because of a given patient’s economic circumstance and associated payment issues.

As healthcare professionals, we must continually be aware that many infectious diseases that we no longer consider to be routine problems — and diseases that are no longer common in the United States — are only a plane ride away. Measles and mumps are common in Europe. Rubella is routine (outside the United States) worldwide. Diphtheria has been a problem in Russia and many of the former countries of the Soviet Union. Hepatitis is at relatively high incidence in Africa and much of Asia, as well as in the Philippines and in certain parts of the Caribbean. Polio is not uncommon in sub-Saharan Africa and the Indian subcontinent. Keep in mind that San Diego had a measles outbreak only a few years ago. Mumps began to increase in incidence in June 2009 in New York City and in New Jersey, and is currently resurging, reported to be spreading primarily through the Orthodox Jewish communities.

Each example of either a local or national epicenter of a given infectious disease — especially one that is effectively controlled by vaccination — reminds us of the ongoing need for vaccination and the advantages of herd immunity. As a society we must do a better job, both politically through legislation and professionally through our representation of the advantages and safety of routine vaccinations in our practices. The pertussis outbreak we are experiencing in California — and the deaths this year of nine infants — serves as a strong and immediately proximal reminder of the need for continued, effective vaccination programs.