February 2, 2016
The Windsor-Essex County Health Unit (WECHU) is following up a confirmed case of pertussis in the Comber area. We would like to take this opportunity to provide a brief update on identifying pertussis, sending appropriate specimens for testing and public health management of the suspect and probable cases of pertussis.
History of pertussis & immunization
Pertussis outbreaks tend to be cyclical in nature with increased disease activity approximately every 4 – 6 years1. Protection against pertussis is not lifelong and wanes after 7-20 years of natural infection and approximately 4-12 years after vaccination with either whole cell or acellular pertussis vaccine (varies with age)2. Young infants (<6 months of age) have the highest risk of mortality and this risk is greatest before they are eligible to receive the vaccine or before completion of their primary vaccine series.
What does this mean in clinical practice?
Under the health promotion and protection act (HPPA), physicians are required to report when they have formed the opinion that an indiviudal has or may have a reportable disease (e.g., pertussis). Physicians when treating their patient should consider pertussis in the differential diagnosis of patients presenting with symptoms compatible with pertussis. However, laboratory testing, using nasopharyngeal (NP) swabs, should only be done on patients with clinical signs and symptoms4 ,5.
Clinically compatible signs and symptoms:
- Paroxysmal cough of any duration OR
- Cough ending in vomiting (without any other cause), or associated with apnea OR
- Cough with inspiratory “whoop” OR
- Any cough illness lasting two weeks or more
Information about taking NP swabs for pertussis
When suspecting a case of pertussis, use a Bordetella pertussis N-0052 testing kit to collect NP swab and request Bordetella testing from the Public Health Lab Customer Service at 1-877-604-4567. A limited number of kits a available from the Health Unit at 519 258-2146 extension 1420.
ONLY test patients with signs and symptoms of pertussis.
Testing asymptomatic persons who are household contacts of a person with pertussis should be avoided as the PCR assay is very sensitive and picks up low levels of DNA (e.g. even non-viable bacteria located in the nasopharynx).
Understanding and interpreting testing results
Positive PCR results should be interpreted in conjunction with the presence of clinical signs and symptoms consistent with pertussis and available epidemiological information (i.e. household contact of a confirmed case of pertussis with incomplete immunization history).
Considerations regarding Pertussis Clinical Management
Management of the case:
Treatment of the case should be based on symptoms of early pertussis – efficacy is related to early treatment (i.e. it is unlikely to be beneficial after 21 days since initial contact). Early treatment is important as it will not reduce symptoms unless given prior to or early in the paroxysmal cough stage of the illness.6 However, untreated symptomatic cases of pertussis whose PCR results are positive should be started on treatment regardless of time since symptom onset. Cases are not considered infectious after 5 days of effective antimicrobial treatment. The recommended antimicrobial agents for treatment or chemoprophylaxis are azithromycin, clarithromycin and erythromycin.
Consideration for contacts management and chemoprophylaxis:
- Pertussis is highly contagious and contacts of the case may require chemoprophylaxis. Public health can provide guidance on contact management. Current recommendations as per the Canadian pertussis control guidelines1 identify that chemoprophylaxis should only be provided to:
- household contacts (including attendees at family day care centres) where there is a vulnerable person defined as an infant < 1 year of age [vaccinated or not] or a pregnant woman in the third trimester
- for out of household exposures, vulnerable persons, defined as infants less than one year of age regardless of immunization status and pregnant women in their third trimester who have had face-to-face exposure and/or have shared confined air for > 1 hour
Chemoprophylaxis is only recommended in the above identified contacts, even in communities that refuse immunization. It should be implemented as soon as possible after exposure as efficacy is related to early implementation. It is not likely to be beneficial after 21 days since the first contact1.
- The on time administration of the 2,4 & 6 month doses of acellular pertussis vaccine are most critical in reducing infant mortality and hospitalization rates from pertussis1,2.
- Up to date vaccine status would vary with age. Current schedule for acellular pertussis vaccine is 2,4,6, and 18 months, 4-6 years and 14-16 years. Adults should be considered up to date if they have received one dose of pertussis containing vaccine (Tdap) in their adulthood (18 years of age and older).
- Acellular pertussis vaccines in Canada have an 85% estimated efficacy which is why infants <1 year, regardless of vaccination should receive chemoprophylaxis when exposed3.
- Vaccination is not recommended for outbreak management, but the outbreak provides an opportunity for patient education and to update the whole family’s vaccination status.
If you have further questions or concerns, please contact the Windsor-Essex County Health Unit at (519) 258-2146, ext. 1447 or ext. 1430.
Dr. S. Wajid Ahmed, MBBS, MAS, MSc, FRCPC
Associate Medical Officer of Health
- National Consensus Conference on Pertussis – Canada Communicable Disease Report ISSN 1188-4169, Volume: 2953 April 2003
- Wendelboe, A M, Van Rie, A, Salmaso, S & Englund, J A. Duration of Immunity Against Pertussis After Natural Infection or Vaccination
- Pertussis Vaccine – Canadian Immunization Guide Seventh Edition – 2006
- CDC-Best Practices for Health Care Professionals on the use of Polymerase Chain Reaction (PCR) for Diagnosing Pertussis
- California Department of Public Health – February 2011 Pertussis: Laboratory Testing
- Heymann, David, e. (2008).Control of Communicable Diseases Manual,19th edition, Washington: American Public Health Association.
- Public Health Ontario, Public Health Laboratory- London, May 25, 2012.