The California Pertussis Epidemic, 2010

Interesting--

OBJECTIVE:
In 2010, California experienced the highest number of pertussis cases in >60 years, with >9000 cases, 809 hospitalizations, and 10 deaths. This report provides a descriptive epidemiologic analysis of this epidemic and describes public health mitigation strategies that were used, including expanded pertussis vaccine recommendations.
STUDY DESIGN:
Clinical and demographic information were evaluated for all pertussis cases with onset from January 1, 2010, through December 31, 2010, and reported to the California Department of Public Health.
RESULTS:
Hispanic infants younger than 6 months had the highest disease rates; all deaths and most hospitalizations occurred in infants younger than 3 months. Most pediatric cases were vaccinated according to national recommendations, although 9% of those aged 6 months to 18 years were completely unvaccinated against pertussis. High disease rates also were observed in fully vaccinated preadolescents, especially 10-year-olds. Mitigation strategies included expanded tetanus, diphtheria, and acellular pertussis vaccine recommendations, public and provider education, distribution of free vaccine for postpartum women and contacts of infants, and clinical guidance on diagnosis and treatment of pertussis in young infants.
CONCLUSIONS:
Infants too young to be fully vaccinated against pertussis remain at highest risk of severe disease and death. Data are needed to evaluate strategies offering direct protection of this vulnerable population, such as immunization of pregnant women and of newborns. The high rate of disease among preadolescents suggests waning of immunity from the diphtheria, tetanus, and acellular pertussis series; additional studies are warranted to evaluate the efficacy and duration of protection of the diphtheria, tetanus, and acellular pertussis series and the tetanus, diphtheria, and acellular pertussis series.

Hmmm-- "Most pediatric cases were vaccinated according to national recommendations" & "Infants too young to be fully vaccinated against pertussis remain at highest risk of severe disease and death."

A comment on the article from Caroline Soyemi, RN, MSN:

Winter et al¹ describe the clinical and epidemiologic characteristics of the 2010 California pertussis epidemic. They illustrate high disease burden and mortality in Hispanic patients, especially among infants, despite comparable vaccination coverage. The authors speculate that the high burden of disease in Hispanic patients might be caused by having larger households and possibly more contacts. Because the inference of a causal relationship between household size and high pertussis burden among Hispanics was not supported by data in this study, it would be beneficial if the authors considered doing an ecologic analysis by geocoding cases to census tract, aggregating case count by census tract, then using the census tract economic and housing data to understand factors that could further explain the high burden of disease as demonstrated in a similar study in which the authors used county-wide coverage levels.²

Previous investigators have demonstrated that occupational exposures to pertussis occur frequently in pediatric health care settings³ and that vaccination of health care personnel (HCP) is cost effective.⁴ The authors did not discuss the role that HCP might have played in the epidemic because they usually are the first to come in contact with infants, and infected HCP may be a source of infection.

Previous authors have demonstrated the presence of other Bordetella species in outbreaks ⁵ and thatBordetella parapertussis infections may contribute to cases thought to be vaccine failures. ⁶ Of the confirmed cases in this outbreak, 82% were laboratory-confirmed by polymerase chain reaction testing. Because this was a large outbreak with several thousands of cases, epidemiologic and clinical distribution of cases by species type would add to the growing body of literature and help readers understand whether there are changes in the spectrum of diseases caused by other Bordetella species.

I wonder about the effect of poverty on Pertussis-susceptibility, given that Hispanics in California, tend to be lower-income.

Hmmm:

Pertussis is a disease of the wealthy, according to the data from the California Department of Public Health. Their latest report, with data on the whooping cough epidemic in California through Nov. 9, 2010, contains the case counts and case rates by county. When those data are combined with data from the Census Bureau on the Latino population of California counties and the Department of Agriculture on median county income, a picture begins to emerge about the real demographics of this illness outbreak.

Twenty California counties have reported 100 or more cases of pertussis in 2010. Those counties contain 85 percent of the state's population, and 88 percent of the state's Latino population. They have reported, in total, 5,900 cases of whooping cough out of the state total of 6,631 cases.

Latinos have been the subject of intense speculation because the California Department of Public Health is reporting that the epidemic appears to be affecting Hispanic infants more than other races. CDPH only has hospitalization information on 40 percent of the cases and draws their conclusions on the epidemic's effects from those limited data.

Internet comments have accused illegal immigrants of being the source of the epidemic. Even officials at the Centers for Disease Control have suggested that Hispanic families have unique living conditions that are contributing to the epidemic.

Of the 20 California counties reporting over 100 cases of pertussis, eight have a higher percentage of Latino residents than the state's rate of 32 percent. These counties have about 44 percent of the state's residents, and are 58 percent Latino. These counties have reported 2,686 cases, 41 percent of the state's total. The average median income for these counties, as of 2008, was 25 percent lower than the statewide median income.

The remaining 12 California counties have Latino populations lower than the state average. They hold 41 percent of the state's population but only have a 29 percent Latino population. They have reported 3,214 cases of whooping cough, 49 percent of the state's total. These same 12 counties have an average median income that is 14 percent higher than the state's.

The CDPH weekly report has been showing for several weeks that whites have the highest rate per 100,000 for whooping cough infection in all age groups over 6 months. Hispanics have the highest rate in infants.

Infants do not receive their first vaccination for pertussis until age 2 months. About 600 cases have been reported in infants too young to have been immunized. The second immunization at four months and the third at six months both demonstrate a drop in cases numbers after they have been received.

The California whooping cough epidemic seems to be heaviest in areas that have fewer Latinos than the statewide average, and that have a median income well above the statewide average. It appears that income and race do play a role in the California epidemic, with well-to-do white people being the center of the outbreak.

Some comments about the Pertussis vaccine from Meryl Nass, MD:

Whooping cough is endemic, but seems to be increasing; looking at the vaccine role

Pertussis (whooping cough) cases are occasionally vaccine-resistant.

Sometimes what looks like pertussis is a related disease, parapertussis, and the pertussis vaccine is useless at preventing this infection.  In fact, the vaccine may actually enhance nasal carriage with parapertussis strains.

Usually, vaccine-induced protection is weak and doesn't last long.

Clearly a new vaccine that is safe and much more effective is sorely needed, for both conditions perhaps, but certainly for Bordetella pertussis (the bacteria that cause whooping cough).  Instead we are likely to be told to keep getting more frequent doses of the clunker vaccine.