Pertussis (whooping cough) is a highly contagious infection of the respiratory tract caused by the bacterium Bordetella pertussis. The National Advisory Committee on Immunization (NACI) recommends immunization against pertussis.
Bordetella pertussis is a Gram-negative aerobic bacterium. Pertussis is primarily a toxin-mediated disease in which toxins produced by the bacteria are responsible for the majority of its clinical features.
The clinical course of pertussis is divided into three stages. The initial catarrhal stage is characterized by runny nose, sneezing, low-grade fever, and a mild cough, similar to a cold. After 1 to 2 weeks of gradually worsening cough, the paroxysmal stage begins.
The paroxysmal stage is characterized by bursts of rapid coughing, ending with an inspiratory whoop and sometimes post-tussive vomiting. This stage can last from 2 to 8 weeks. In the convalescent stage, recovery is gradual and may take weeks to months.
The clinical course varies with age. In young infants, who are at the highest risk, clinical symptoms are frequently atypical. Whoop and post-tussive vomiting may be absent. The presentation may be characterized solely by episodes of apnea. Serious complications occur mainly in infants and may include pneumonia, atelectasis, seizures, encephalopathy, hernias and death.
Pertussis may be milder in adolescents and adults but symptoms can range from asymptomatic infection to a very prolonged, debilitating cough. Pertussis is a common and often unrecognized cause of cough persisting for over 2 weeks in adolescents and adults.
Complications in adolescents and adults include sleep disturbance, rib fractures, subconjuctival haemorrhages, rectal prolapse, and urinary incontinence, all from intense and persistent coughing. Adolescents and adults with a cough, and less so in those who are asymptomatic, are a source of infection for those most at risk, namely infants.
Pertussis is highly communicable with studies showing 80% secondary attack rates among susceptible household contacts. Pertussis is usually transmitted by the respiratory route through inhalation of respiratory droplets; indirect spread through contaminated objects occurs rarely, if at all. The incubation period is 9 to 10 days (range, 6 to 20 days) and may rarely be as long as 42 days.
Infectiousness is greatest during the catarrhal stage and during the first 2 weeks after cough onset. In general, an individual should be considered infectious from the beginning of infection to 3 weeks after onset of coughing, if not treated with antibiotics. Patients are no longer contagious after 5 days of appropriate antibiotic treatment.
Pertussis is endemic worldwide and occurs year round, even in regions with high vaccination coverage. The World Health Organization (WHO) has estimated that, there are between 20-40 million cases of pertussis worldwide, 95% of which were in developing countries.
Incidence rates are highest among young children in countries where vaccination coverage is low. With approximately 400,000 deaths per year, pertussis remains one of the leading causes of death among non-immunized children, mainly in developing countries.
As a result of widespread immunization programs, proper nutrition and good medical care pertussis incidence has decreased in high income countries.
Highest pertussis rates are typically reported in unimmunized infants and adolescents, while mortality is rare in industrialized countries and is estimated to occur in 1 out of every 1000 unprotected children, the most vulnerable cohort. Pneumonia is the most common cause of death, principally occurring in infants less than 6 months of age.
Information about immunization requirements and recommendations related to travel can be found in the Canadian Immunization Guide.
Pertussis can affect individuals of any age; however, severity is greatest among infants who are too young to be protected by a complete vaccine series. Young infants are also at highest risk of pertussis-associated complications.
Immunity to pertussis from childhood vaccination and natural disease wanes with time; therefore, adolescents and adults who have not received a booster vaccination are at risk of infection and its consequent transmission of the bacteria to others.
Pertussis can be prevented by immunization. Primary immunization for all children is recommended at 2, 4 and 6 months of age. Booster doses are recommended at 12 to 23 months (generally given at 18 months of age), 4 to 6 years, and 14 to 16 years of age.
One dose of acellular pertussis-containing vaccine (Tdap) vaccine should be administered to adults if they have not previously received pertussis vaccine in adulthood (18 years of age and older).
For further information about the immunization recommendations, please refer to the most recent version of the Canadian Immunization Guide.
Cases of pertussis should be reported to the local health authority. Confirmed and suspected cases should be isolated from young children and infants until the patients have received at least 5 days of antibiotics.
Suspected cases who do not receive antibiotics should be isolated for 3 weeks after onset of paroxysmal cough or until the end of cough, whichever comes first.
Contacts, especially children, must have their immunization status verified. If immunization status is incomplete and no contraindications are identified, recommended doses of vaccine should be given.
In special circumstances, such as a regional outbreak situation, immunization with Tdap may be offered to pregnant women (≥26 weeks of gestation) irrespective of their immunization history.
When an outbreak is occurring, vaccinating pregnant women increases maternal antibody transfer providing immediate protection to the vulnerable newborn who is not yet immunized. Vaccinating pregnant women also prevents them from acquiring infection that they may pass onto their newborn baby.
Specific disease management and control guidelines may be available at the provincial, territorial, or local level.
Pertussis is a cyclical disease, which peaks at two to five year intervals. With the introduction of whole cell pertussis vaccine in 1943, the incidence of pertussis decreased significantly, from an average of 156 cases per 100,000 population in the five years prior to vaccine introduction, to a low of 5 cases per 100,000 (2005 to 2011). Refer to Figure 1.
A resurgence of pertussis was observed beginning in 1990, likely due to a combination of factors including:
The whole cell pertussis vaccines were replaced with acellular pertussis vaccines in 1997/1998, which was followed by a steady decline incidence to 2.0 cases per 100,000 in 2011.
A seven-fold increase in national incidence to 13.9 per 100,000 was observed in 2012, due to outbreaks in multiple jurisdictions across the country.
The incidence of pertussis is highest in infants and children, and decreases significantly in those older than 14 years (refer to Figure 2).
The highest mean incidence rates from 2005 to 2011 were:
Following the introduction of a single adolescent dose of acellular pertussis vaccine in 2004, between 2005 and 2011, the incidence of pertussis decreased in all age groups, most notably among those aged 10 to14 years (84% decrease) and those aged 15 to 19 years of age (81% decrease).
During the 2012 outbreak, increases in incidence were observed across all age groups nationally, with the highest incidence rates in those less than one year (120.8 per 100,000; n=460) and those 10-14 years of age (64.1 per 100,000; n=1203).
Hospitalization and death are more common among infants, particularly those 3 months of age or less.
One to four deaths related to pertussis occur each year in Canada, typically in infants who are too young to be immunized, or children who are unimmunized or only partially immunized.
More detailed information on the epidemiology of pertussis in Canada can be found in the Canadian Communicable Diseases Report.
*Case data from 1924 to 2011 were obtained from the Canadian Notifiable Diseases Surveillance System. Case data for 2012 were obtained directly from provinces and territories by CIRID and are preliminary. PEI did not report 1924-1928; Newfoundland did not report until 1949; Yukon did not report 1924-1955; Northwest Territories did not report 1924-1958; Nunavut data for 1999 are only partial, for 2007 & 2009 are missing, and for 2008, 2010-2011 are preliminary
*Case data from 1980 to 2011 were obtained from the Canadian Notifiable Diseases Surveillance System. Case data for 2012 were obtained directly from provinces and territories by CIRID and are preliminary. Nunavut data for 1999 are only partial, for 2007 & 2009 are missing, and for 2008, 2010-2011 are preliminary; Population data (July 1st annual estimates) was obtained from Statistics Canada.
Health professionals in Canada play a critical role in identifying and reporting cases of pertussis. See the Surveillance section for more information on pertussis surveillance in Canada.