PERTUSSIS IN WEST MARIN: Our Own Epidemic

Michael Witte, MD, and David Bunnett

Pertussis, commonly called whooping cough, is a highly contagious disease that is potentially fatal for infants and small children. Seventy years ago, it was a leading cause of infant mortality in the United States, but within just a few years after that, effective vaccinations had nearly eliminated it as a major public health concern. Now, whooping cough is making an unwelcome comeback. In 2010, Marin County--listed by the Centers for Disease Control as the healthiest county in the United States--had the highest incidence of pertussis in California, a rate high enough to qualify as an epidemic.

This remarkable local story begins with some historical context. Up to the early 1940s, reported cases of pertussis were as high as 250,000 per year in the United States, with as many as 9,000 yearly deaths, mostly of infants. Because of population growth since then, today those rates would be equivalent to 590,000 annual cases and 21,000 yearly deaths. Thanks to vaccinations, however, the average national incidence of pertussis had been reduced to around 2,900 cases by the 1980s.

Unfortunately, the prevalence of pertussis has been gradually increasing in the last two decades, for reasons that are not entirely clear. One contributing cause may be that the pertussis vaccine was reformulated as an acellular vaccine to reduce the reaction to the injection itself: the original whole-cell vaccine had caused redness, swelling and pain for up to half the children receiving it. The newer, gentler vaccine is effective, but it appears to be less long-lasting than the previous formula. Another cause may be the choice of some parents not to vaccinate their children for a variety of reasons, including religious beliefs, alternative medical ideas, or concern about the safety of the vaccine itself.

Whatever the cause, the more recent facts and figures about pertussis are disturbing. In 2010, there were 27,550 new pertussis cases and 27 deaths reported nationwide--a 10-fold increase compared to the 1980s average. The 2010 epidemic was especially severe in California, which had over one-third of all U.S. cases and 10 of the deaths. Within California in 2010, the greatest incidence of pertussis was in Marin County. At 138.4 cases per 100,000 population, Marin’s incidence rate was nearly six times the state average. There were 351 total cases in Marin that year, but thankfully no deaths.

Marin was hit hard in 2010--in terms of incidence rate, harder than any county in the state. As the CDC cautions, this fact cannot be definitively attributed to a single cause. Geographically, there was some randomness in where outbreaks occurred. Urban areas were more likely to suffer at least some exposure to an infectious outbreak, and some of the more sparsely populated counties (Alpine, Modoc, Sierra, Trinity) reported no pertussis cases at all in 2010. On the other hand, Mono County was also very hard hit, while the biggest cities reported an incidence of pertussis far below that of Marin-- about one-eighth Marin’s rate for San Francisco, and about one-tenth for Los Angeles.

While there is randomness in the geographic distribution of outbreaks, there is no lack of clarity about what caused the overall risk of pertussis to decline so much since 1945: it was the vaccinations. Indeed, California state law requires children entering kindergarten to show proof of vaccination. However, parents who do not want their child vaccinated can avoid this requirement by signing a Personal Belief Exemption (PBE). According to Marin County Immunization Coordinator Sharayn Forkel, in 2010 the statewide average rate of children with PBEs was 2.3%, whereas the Marin County rate was 7.1%--more than three times the state average.

Again, the CDC is cautious about attributing the increase in pertussis to specific causes. But at the very least, the comparison of Marin’s 2010 incidence of pertussis (highest in the state) with Marin’s rate of unvaccinated schoolchildren (more than three times the state average) is worthy of attention. Even more worthy of attention are the following statistics from West Marin, where Dr. Witte practices:

• Percentage of children entering kindergarten in Bolinas-Stinson School in 2011 who had a PBE for one or more vaccines: 27%

• Percentage of children entering kindergarten in Lagunitas School in 2011 who had a PBE for one or more vaccines: 50%

These PBE rates for pertussis and other vaccines should set off all kinds of alarms among those concerned with public health.

Many parents who choose not to vaccinate their children are betting that because certain formerly common diseases are now rare, their child can skip the vaccinations and still not get the diseases. In individual cases, they might win that bet.

The concept of “herd immunity” is central to this belief. Under this logic, assume that a certain (high) percentage of a community has protection against getting an infectious disease, through either having had the disease and survived it, or having been vaccinated successfully against it. In that case, the prevalence of the disease drops to near zero, since the germ can’t find enough susceptible hosts to carry it around and keep it alive.

Often without being consciously aware of it, parents who rely on herd immunity to protect their children are counting on most other parents vaccinating their kids, so that the disease won’t survive and spread in their part of the “herd.” Ms. Forkel, the immunization coordinator, is not fond of this strategy. She points out that only about 10-15% of the population can forgo immunization before herd immunity is lost. That margin should be reserved for newborns, those who truly can’t tolerate vaccination due to allergies or physical frailty, and those without access to vaccinations. Generally healthy individuals who choose not to be vaccinated are putting others at risk, not just themselves. When the number protected by vaccinations drops below about 85%, the germ finds enough available hosts to keep it alive and traveling around. This is likely what happened in Marin in 2010.

Larry Enos, superintendent of both the Bolinas-Stinson and Lagunitas school districts, says that Bolinas-Stinson parents have substantially reduced their use of PBEs this year. In Lagunitas, the rate of 7th graders with PBEs declined from 41% in 2011 to 28% in 2012. On the other hand, of the 25 new kindergarten students starting at San Geronimo School in September 2012, 56% had exemptions to some or all of the required immunizations due to PBEs.

Enos was diplomatic in his statements about the vaccination controversy. He made it clear that he absolutely respects both the sincerity and the legal rights of parents who choose not to vaccinate. But he also added: “I would hope that people will consider carefully before refusing immunization for their children.”

In an influential article on improving vaccination rates published earlier this year, Dr. Douglas Diekema found inspiration in the ancient Greek philosophers: “In The Art of Rhetoric, Aristotle argued that persuasion requires not only a reasonable argument and supporting data, but also a messenger who is trustworthy and attentive to the audience and a message that engages the audience emotionally. Data and facts, no matter how strongly supportive of vaccination, will not be sufficient to compete with the opposition's emotional appeals. The use of a compelling story about a single victim of vaccine-preventable illness is far more likely than data to move an audience to action.”[1]

In Marin County, we are blessed with some of the best health and healthcare in the United States. The diseases that used to kill or infect many infants and children have been removed from the community and from parents’ fears. Those fears of disease have been replaced by a fear of hurting their most precious responsibility, their baby, with a perceived unnecessary danger of immunizations.

Our job as physicians is twofold. On the one hand, we need to present the science behind the immunization risk, the true risk/benefit ratio of vaccines and the concept of herd immunity. On the other hand, we should also convey stories of the dangers our grandparents faced with their children. Most importantly, through motivational interviewing and other techniques, we should respect their fears and the information they come to us with. If we engage our patients emotionally, we are more likely to persuade them to vaccinate their children.

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Pertussis: The Clinical Picture

Symptoms

Initial symptoms of pertussis (whooping cough) may resemble a common cold. A persistent cough typically develops after a week or two. Long, convulsive bouts of numerous, rapid coughs are interspersed by a characteristic high-pitched whoop as the patient attempts to draw a breath. During coughing episodes, the patient may turn blue. Vomiting and exhaustion often follow coughing episodes.

The intensive coughing stage typically lasts from 1 to 6 weeks but can extend as long as 10 weeks. During convalescence, coughing episodes may recur for a period of months.

Symptoms may be milder in older children or adults. However, they may still transmit the disease to others, especially unimmunized or partially immunized infants and young children.

Complications

Children less than six months of age are the most likely to develop complications. The most common is bacterial pneumonia, which is also the primary cause of deaths from pertussis. Possible complications may include seizures, ear infections, and dehydration, among others. For adults, rib fracture from coughing is also possible.

Preventive measures

Pertussis is highly communicable. It is transmitted primarily through contact with respiratory droplets--that is, by coughing or sneezing. It can also be spread by contact with freshly contaminated objects.

The DTaP vaccination is the best defense against pertussis (or TDaP, slightly differently formulated for older children and adults). Babies are normally vaccinated at two months, and are defenseless before that. Pregnant women and families with young babies are advised to make sure that adults and older children who will be in contact with the infant are protected by up-to-date vaccinations. Ideally, all family members of babies under 2 months should be immunized against pertussis to “passively” protect the baby.

Good coughing etiquette (cover the mouth and turn away when coughing or sneezing) and hand washing are simple ways to reduce transmission of many communicable diseases, including pertussis.

Diagnosis

Pertussis has three clinical phases: catarrhal, paroxysmal and convalescent. The catarrhal phase acts like the common cold, but is prolonged, and then followed by the paroxysmal coughing phase which can last several weeks. Patients who have been immunized may still get symptoms, but they are typically milder. Laboratory testing by culture or PCR testing of the deep nasopharynx is most reliable early in the catarrhal phase. The problem with this approach is that suspicion of pertussis often doesn’t arise until the paroxysmal phase, when the tests are less reliable.

Treatment

Antibiotic treatment of pertussis has only shown to be clearly effective within 21 days of the onset of symptoms. This would mostly be true then in the early catarrhal stage. The emphasis in treatment being early should mean that family members and others likely exposed should be treated at the first onset of symptoms. Macrolide antibiotics, erythromycin, clarithromycin and azithromycin are all effective against pertussis. Trimethoprim-sulfa is also effective as an alternative.

Where to get vaccinations

For access to vaccinations in West Marin, regardless of ability to pay, patients should contact the Coastal Health Alliance at these numbers:

• Point Reyes Station: 415-663-8666

• Bolinas: 415-868-0124

• Stinson Beach: 415-868-9656

Elsewhere in the county, patients should contact their regular primary care provider for a TDaP booster shot. For uninsured patients who have difficulty affording the TDaP immunization, a limited number of free vaccines are available at several clinic sites throughout the county.

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Dr. Witte, a pediatrician and family physician, is medical director of the Coastal Health Alliance in western Marin County. Mr. Bunnett serves on the board of directors of the Alliance and writes for the West Marin Citizen, where portions of this article originally appeared.

Emails: mikew@coastalhealth.net, dtbunnett@earthlink.net

References

1. Diekema DS, “Improving childhood vaccination rates,” NEJM, 366:391-393 (2012).