From pertussis to tuberculosis: what can be learned?

Burden and Outcomes of Severe Pertussis Infection in Critically Ill Infants

OBJECTIVES

Despite World Health Organization endorsed immunization schedules, Bordetella pertussis continues to cause severe infections, predominantly in infants. There is a lack of data on the frequency and outcome of severe pertussis infections in infants requiring ICU admission. We aimed to describe admission rates, severity, mortality, and costs of pertussis infections in critically ill infants.

DESIGN

Binational observational multicenter study.

SETTING

Ten PICUs and 19 general ICUs in Australia and New Zealand contributing to the Australian and New Zealand Paediatric Intensive Care Registry.

PATIENTS

Infants below 1 year of age, requiring intensive care due to pertussis infection in Australia and New Zealand between 2002 and 2014.

MEASUREMENTS AND MAIN RESULTS

During the study period, 416 of 42,958 (1.0%) infants admitted to the ICU were diagnosed with pertussis. The estimated population-based ICU admission rate due to pertussis ranged from 2.1/100,000 infants to 18.6/100,000 infants. Admission rates were the highest among infants less than 60 days old (p < 0.0001). Two hundred six infants (49.5%) required mechanical ventilation, including 20 (4.8%) treated with high-frequency oscillatory ventilation, 16 (3.8%) with inhaled nitric oxide, and 7 (1.7%) with extracorporeal membrane oxygenation. Twenty of the 416 children (4.8%) died. The need for mechanical ventilation, high-frequency oscillatory ventilation, nitric oxide, and extracorporeal membrane oxygenation were significantly associated with mortality (p < 0.01). Direct severe pertussis-related hospitalization costs were in excess of USD$1,000,000 per year.

CONCLUSIONS

Pertussis continues to cause significant morbidity and mortality in infants, in particular during the first months of life. Improved strategies are required to reduce the significant healthcare costs and disease burden of this vaccine-preventable disease.

Immune response genes modulate serologic responses to Vibrio cholerae TcpA pilin peptides

Cholera is an enteric disease caused by Vibrio cholerae. Toxin-coregulated pilus (TCP), a type 4 pilus expressed by V. cholerae, is a cholera virulence factor that is required for host colonization. The TCP polymer is composed of subunits of TcpA pilin. Antibodies directed against TcpA are protective in animal models of cholera. While natural or recombinant forms of TcpA are difficult to purify to homogeneity, it is anticipated that synthesized TcpA peptides might serve as immunogens in a subunit vaccine. We wanted to assess the potential for effects of the immune response (Ir) gene that could complicate a peptide-based vaccine. Using a panel of mice congenic at the H-2 locus we tested the immunogenicity of TcpA peptide sequences (peptides 4 to 6) found in the carboxyl termini of both the classical (Cl) and El Tor (ET) biotypes of TCP. Cl peptides have been shown to be immunogenic in CD-1 mice. Our data clearly establish that there are effects of the Ir gene associated with both biotypes of TcpA. These effects are dynamic and dependent on the biotype of TcpA and the haplotypes of the host. In addition to the effects of the classic class II Ir gene, class I (D, L) or nonclassical class I (Qa-2) may also affect immune responses to TcpA peptides. To overcome the effects of the class II Ir gene, multiple TcpA peptides similar to peptides 4, 5, and 6 could be used in a subunit vaccine formulation. Identification of the most protective B-cell epitopes of TcpA within a particular peptide and conjugation to a universal carrier may be the most effective method to eliminate the effects of the class II and class I Ir genes.