Molecular epidemiology of the pertussis epidemic in Washington State in 2012

Dominance of two genotypes of Bordetella pertussis during a period of increased pertussis activity in Alberta, Canada: January to August 2012

OBJECTIVES

The purpose of this study was to undertake an epidemiological analysis of an increase in Bordetella pertussis activity during the period January 1 to August 31, 2012 in Alberta, Canada. B. pertussis testing was done using an IS481 real-time PCR assay with PCR-positive and indeterminate specimens cultured and stored for further analysis.

METHODS

Laboratory data were linked to Alberta Health (AH) cases that were reported in the Communicable Disease Reporting System (CDRS) to identify case isolates; exclusion criteria were used to avoid biases. Case isolates were analyzed at the National Microbiology Laboratory (NML) by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Pertussis immunization data were extracted from the Alberta Provincial Immunization Repository (Imm/ARI) and linked to the pertussis cases.

RESULTS

Using PFGE and MLST, 52 case isolates could be divided into two main sequence type groups: 41 cases belonged to the ST-1 group (ST-1 and the novel ST-19) and 11 cases belonged to the ST-2 group (ST-2 and the novel ST-20). Of the total cases genotyped (N=52), 18 (34.6%) had a history of immunization, 28 (53.8%) were not immunized, and six (11.6%) had an unknown immunization history. Of the total non-immunized cases, 25/28 (89.2%) belonged to the ST-1 group. Furthermore, of the 41 ST-1 group cases, 25 were not immunized compared to only three of the ST-2 group cases (p=0.0004, Fisher's exact test).

CONCLUSIONS

This study shows the dominance of two genotypes of B. pertussis in our jurisdiction and indicates less pertussis immunization in individuals infected with the ST-1 group.

Pertussis outbreak, southeastern Minnesota, 2012

OBJECTIVE

To describe clinical and laboratory findings from the 2012 southeastern Minnesota pertussis outbreak.

PATIENTS AND METHODS

Patients were selected for 2 parts of the study. In the first part, nasopharyngeal swabs from a convenience sample of 265 unique patients were used for both the clinician-requested polymerase chain reaction (PCR) test and culture. B pertussis isolates were tested for macrolide susceptibility and typed using whole genome sequencing and pulsed-field gel electrophoresis. Pertactin gene sequences were analyzed to identify pertactin-deficient B pertussis. In the second part, all patients seen at Mayo Clinic in Rochester, Minnesota, who had PCR results positive for Bordetella pertussis or Bordetella parapertussis between January 1, 2012, and December 31, 2012, were analyzed for patient demographic features and vaccination records.

RESULTS

One hundred sixty patients had results positive for B pertussis, and 21 patients had results positive for B parapertussis. Among the 265 swabs cultured, B pertussis was detected by both culture and PCR in 11. One swab was positive for B pertussis by culture alone, and 13 were positive by PCR alone. Polymerase chain reaction detected B pertussis more frequently than did culture (P=.001). No macrolide resistance was detected. All 12 isolates tested had an altered pertactin gene, including 9 with a signal sequence deletion, 2 with insertion sequence disruptions, and 1 with a premature stop codon. Nine and 3 isolates were pertactin types prn1 and prn2, respectively. Whole genome sequencing and pulsed-field gel electrophoresis detected the presence of multiple B pertussis strains. The mean age of patients with pertussis was younger than that of those without pertussis (15.6 and 25.5 years, respectively; P=.002). Compared with those whose test results were negative for B pertussis, fewer patients with positive results had received whole-cell pertussis vaccine (P=.02). In the subgroup who had received acellular vaccine exclusively, the time since the most recent pertussis vaccination in those with results positive for B pertussis was longer than that in those with negative results (1363 vs 1010 days; P=.004).

CONCLUSION

The 2012 pertussis outbreak in southeastern Minnesota included multiple strains of B pertussis, all putatively lacking pertactin. Our findings may indicate decreased efficacy of (and waning immunity from) acellular vaccines as contributors to the outbreak.