Statement on management of persons exposed to pertussis and pertussis outbreak control

Jointly issued by the National Advisory Committee on Immunization, the Advisory Committee on Epidemiology and the Canadian Paediatric Society.

Canadian Medical Association Journal 1995; 152: 712-716
Health Canada, 1994
Reproduced with permission of the Minister of Supply and Services Canada, 1996

Copies of the original report (Canada Communicable Disease Report 1994; 20: 193-199) can be obtained from Eleanor Paulson, editor, CCDR, Bureau of Communicable Disease Epidemiology, Laboratory Centre for Disease Control, Tunney's Pasture, Ottawa, ON K1A 0L2.
In 1989 and early 1990 a large number of pertussis outbreaks occurred in Canada, with an associated increase in the number of reported cases. During this period requests for guidance in outbreak control were received by health authorities at the provincial and federal levels. In response, the National Advisory Committee on Immunization, the Advisory Committee on Epidemiology and the Canadian Paediatric Society collaborated on the preparation of guidelines designed to assist local and provincial public health officials in the control of pertussis.[1] Provincial health authorities have used these guidelines to manage outbreaks and are accumulating data on their effectiveness and applicability.

A consensus conference on pertussis was held in Hull, Que., May 11 to 13, 1993, sponsored by the Childhood Immunization Division, Bureau of Communicable Disease Epidemiology, Laboratory Centre for Disease Control, Health and Welfare Canada.[2] Recommendations arising from that conference based on data from previous and recent pertussis outbreaks have been used to revise the initial guidelines. The major changes are clarification of the surveillance case definition, addition of a "suspected case" definition for public health intervention and simplification of recommendations for chemoprophylaxis.

Contents

Background

Pertussis (whooping cough) is a highly contagious, acute infectious disease caused by Bordetella pertussis. The illness is characterized by severe paroxysms of coughing, with or without a classic inspiratory whoop; in infants, apnea may be a prominent symptom. Uncomplicated cases have a clinical course lasting from 6 to 10 weeks. A substantial proportion of infants with whooping cough experience complications such as apnea, pneumonia, seizures, encephalopathy and death. Both the rate and severity of complications are greater among infants less than 1 year old. Death occurs in one in every 200 infants less than 1 year old.[3] Pertussis can cause significant illness in older children and adults; in this population, however, clinical manifestations are less severe, the whoop is usually absent, and complications are uncommon.

In susceptible populations over 90% of exposed people will acquire infection and disease.[4] Infection rates among immunized contacts may also be high, but symptoms will be less frequent and severe.[5] Infection with B. pertussis produces long-term immunity from the disease but may not prevent reinfection. A full course of vaccination produces immunity in about 80% to 90% of recipients. Protection from vaccination appears to wane, beginning 3 to 5 years after the last vaccination; no protection is detectable by 10 to 12 years after the last dose of pertussis vaccine. This becomes important for older children and adults. Pertussis vaccination is not generally recommended after the age of 6 years because the incidence and severity of disease decrease with age while vaccine-associated adverse reactions are reported more frequently. Multiple doses of vaccine and regular boosters are required for young children, which limits the usefulness of vaccination as a measure for outbreak control. In addition, immunization with pertussis vaccine, while protecting against disease, prevents neither colonization nor transmission of B. pertussis, and there is evidence of continued circulation of the organism even in well-immunized populations.[6]

Infants appear to derive no protection from their mothers. Pertussis is in this regard unlike many other childhood diseases, in which passively acquired maternal antibodies confer protection during the first few months of life.

Children who have received some but not all of the recommended doses of vaccine, and children who acquire infection despite having completed their immunization schedule, appear to have less severe illness and fewer complications than children who have not been vaccinated.

The incidence of pertussis and its resultant mortality have been reduced by more than 90% through immunization, and overall control is excellent.[7] Despite this, cases and outbreaks continue to occur in Canada because of incomplete immunization coverage, the need for multiple doses of vaccine to achieve protection, the less-than-100% efficacy of the vaccine, the waning of vaccine-induced immunity in people over 6 years of age and continued circulation of the organism.

When outbreaks occur in well-immunized populations it is inevitable that a substantial proportion of cases will occur among individuals who have a history of immunization. It is important not to misinterpret this as a failure of the immunization program.

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Definitions

As a result of inadequate laboratory methods for the reliable diagnosis of pertussis, standard case definitions are necessary for case identification, reporting and intervention. Although no case definition is perfect, the following national case definitions should be used for surveillance, notification, and outbreak identification and management.

Clinical case

Cough lasting 2 weeks or longer and one or more of the following:
  1. Paroxysmal cough.
  2. Cough ending in vomiting or associated with apnea.
  3. Inspiratory "whoop" for which there is no other known cause.

Confirmed case

  1. Laboratory confirmation of B. pertussis regardless of symptoms, or
  2. A clinical case with an epidemiologic link to a laboratory-confirmed case.

Suspect case

  1. Paroxysmal cough of any duration, or
  2. Cough with inspiratory whoop, or
  3. Cough ending in vomiting or gagging, or associated with apnea with no other known cause.

Contact

Although it is important to define contact in order to guide intervention, definitions listing specific settings and durations of exposure are problematic. The definition of significant contact may vary according to the situation. In general, face-to-face contact with someone with the infection (unless it was only for a short period, e.g., less than 5 minutes) and sharing the same confined air space for a prolonged period (e.g., 1 hour) should be considered significant. However, identification of significant contacts must be individualized and take into consideration the degree of risk to the individual and the specifics of the exposure. For example, a significant contact may include an infant being in the same room for an hour with a case or a newborn being directly coughed upon by a case.

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Laboratory confirmation

At present culture is the only standardized test for laboratory confirmation of pertussis and should be performed in a laboratory with a proven capacity for isolating the organism.[8] Nasopharyngeal cultures should be collected by either aspiration or using a calcium alginate swab (cotton swabs must not be used). There is no role for oropharyngeal culture in the diagnosis of pertussis. Nasopharyngeal culture results are likely to be falsely negative if taken more than 21 days after onset of cough, or if the individual is on antimicrobial therapy effective against B. pertussis (e.g., erythromycin, trimethoprim-sulfamethoxazole, tetracycline); therefore, a negative culture result does not preclude the diagnosis of pertussis. Identification of B. pertussis in nasopharyngeal secretions by the polymerase chain reaction technique is in the development stage and may be an acceptable diagnostic method in the future. Because of an unacceptably high rate of false-positive and false-negative results, commercially available direct fluorescent antibody (DFA) tests are of no use and should not be used for case confirmation.[9,10] Asymptomatic people who are only DFA positive (i.e., culture negative) are not considered cases and no follow-up is necessary.

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Roles of physicians and public health authorities in the control of pertussis

Control of pertussis and management of outbreaks requires a close partnership between the primary care physician and public health authorities. Frequent and early two-way communication is essential to identify and control community outbreaks. There are important roles for both primary care physicians and public health authorities in surveillance, outbreak control, and the management of cases and contacts.

Surveillance

Ongoing surveillance for pertussis is important to monitor the incidence of the disease and the effectiveness of vaccine programs and to detect outbreaks occurring in the community. For the purposes of national surveillance, case definitions need to be specific to allow comparison and analysis of epidemiologic factors. To facilitate the identification and management of outbreaks, all suspect cases of pertussis should be reported promptly by physicians to the local public health authority; only cases meeting the surveillance definition (clinical case, confirmed case) need be reported by provincial authorities to the national database.

Outbreak control and management of cases and contacts

There is no simple or widely accepted definition of an outbreak of pertussis. Any definition of an outbreak must take into account the typically cyclical nature of pertussis disease, local patterns and populations affected. Surveillance definitions require a high degree of specificity and are too insensitive and too restrictive (e.g., "a cough lasting 2 weeks or more") to ensure early identification of outbreaks and effective public health intervention. For timely intervention, the suspect-case definition should be used for initial reporting. Criteria for the implementation of public health strategies require a higher degree of certainty and pertain to cases with the following:
  1. Paroxysmal cough or cough with vomiting or gagging for 7 days or more with no other known cause, or
  2. Cough associated with apnea with no other known cause, or
  3. Cough with inspiratory whoop with no other known cause, or
  4. Clinically compatible symptoms and an epidemiologic link with a confirmed case or a setting where there have been cases.

Prompt reporting of suspect cases and consultation with public health authorities will encourage discussion of current recommendations and facilitate implementation of intervention strategies. Public health authorities must take action while awaiting confirmation of the diagnosis. When an increase in the incidence of pertussis is suspected in a particular region, surveillance for cases should be enhanced and appropriate epidemiologic and microbiologic information collected. Active surveillance should be initiated with frequent contact with microbiologic laboratories, hospital emergency departments, hospital admission offices, physicians' offices and schools. This will also heighten awareness of pertussis as a potential cause of cough illness in the community and promote appropriate laboratory confirmation. Because the disease may be atypical in older children and adults, earlier and more frequent use of diagnostic nasopharyngeal cultures should be considered in people presenting with respiratory symptoms during suspected outbreaks.

Goals for outbreak management are to stop transmission in closed settings (such as the family and family day care) and to provide protection against disease for those at highest risk of severe disease and its complications. Prevention of community transmission is likely not feasible.

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Immunization

Assuring complete immunization of all children remains the most important preventive measure in maximizing control of pertussis.[4,11] The physician treating a case should consult with public health authorities and ensure that all household contacts of cases have their immunization updated. Updating immunization of day-care, school and community contacts should be undertaken by public health authorities.

Contacts

Children exposed to a case should have their immunization status reviewed. If immunization is incomplete and in the absence of contraindications, any necessary doses should be given as follows:
  1. Children who have received fewer than three doses should receive their additional dose(s) as quickly as possible, with an interval of 4 weeks between doses.
  2. Children who have had three doses may receive their fourth dose as early as 6 months after the third dose.
  3. A booster dose of vaccine, usually as diphtheria toxoid-pertussis vaccine-tetanus toxoid (DPT), should be given to any child 6 years of age or less who has had four doses of vaccine unless the most recent dose was given within the past 3 years.

In communities with evidence of ongoing pertussis transmission, routine immunization with DPT can begin for children as young as 6 weeks of age and subsequent doses given every 4 weeks. (In such cases, if oral poliovirus vaccine is used, it should be given with the first and third doses of DPT.)

Vaccination is not usually indicated for children 7 years of age or older.

Passive immunization with currently licensed immune globulin has no place in the management of pertussis.

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Management of cases

Cases of pertussis should be treated with erythromycin (40 to 50 mg/kg daily, maximum 1 g/d, for 10 days). Trimethoprim-sulfamethoxazole may be used if erythromycin is not tolerated; however, data demonstrating its effectiveness are limited. Although antibiotics may have little effect on the clinical course once symptoms are established, their use can hasten clearance of the organism and limit spread of the disease. However, beginning antimicrobial therapy beyond 3 weeks after onset of symptoms is of no benefit because the organism is spontaneously cleared from the nasopharynx by that time.

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Management of contacts

Management of contacts is based on the risk of severe disease in the individual who may acquire the infection through a contact and the degree of risk resulting from the contact setting. Children less than 1 year old are at greatest risk of developing severe disease. The risk of acquiring infection, in decreasing order, is as follows:
  1. Family setting.
  2. Family day care.
  3. Day care.
  4. Physicians' waiting rooms, hospital settings.
  5. School.
  6. General community.

All contacts should be identified and interviewed to detect any additional cases. Whenever practical, an attempt should be made to identify the source of infection. Symptomatic contacts should have a thorough medical examination, including nasopharyngeal culture. Pertussis cultures are of no use in asymptomatic contacts for outbreak control or for assessing the need for antibiotics.

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Chemoprophylaxis

The purpose of chemoprophylaxis is to prevent disease in susceptible individuals exposed to a case of pertussis and to decrease transmission to at-risk individuals. Because immunization provides only partial protection and because immunized people can still harbour and transmit B. pertussis, erythromycin therapy of cases and prophylactic treatment of contacts may be beneficial.[4,12]

There have been no controlled, blinded studies of the efficacy of erythromycin in preventing transmission of pertussis to contacts. However, a number of retrospective studies suggest that erythromycin given to contacts within 2 weeks of onset of cough in the index case halts transmission and prevents disease in contacts.[11,13-17]

The physician treating a case of pertussis should notify and consult with public health authorities and ensure that all household contacts, regardless of age and immunization status, are offered chemoprophylaxis.

Public health authorities should be responsible for ensuring that all contacts and caregivers in a family day-care setting are offered appropriate chemoprophylaxis. In other day-care settings, prophylaxis should be undertaken after an assessment of risk. Only nonimmunized contacts and contacts less than 1 year old should routinely receive chemoprophylaxis. Infants less than 1 year old with significant contact in other community settings should also receive chemoprophylaxis. Prophylaxis is most effectively accomplished by providing medication or prescriptions directly rather than advising families to obtain the medication from their own physician.

Chemoprophylaxis should consist of erythromycin, 40 to 50 mg/kg daily (maximum 1 g/d), in divided doses, for 10 days; erythromycin estolate may be the preferred preparation in children. It should be given as soon as possible, and no later than 14 days, after the recipient's first contact with a primary case during the infectious period (in high-risk household exposure settings, chemoprophylaxis may be considered for up to 21 days).

Management of pregnant contacts must be individualized and should be discussed with local experts. Erythromycin is poorly tolerated during pregnancy because of its gastrointestinal side effects. However, infants of mothers who become symptomatic with pertussis up to 2 to 3 weeks before labour have an extremely high risk of disease. Therefore, pregnant household contacts should be offered chemoprophylaxis. If chemoprophylaxis is not tolerated or not complete by the time of delivery, chemoprophylaxis should be given after delivery to both the mother and the newborn.

Erythromycin must be considered for each new episode of close exposure unless the contact was receiving erythromycin at the time of exposure.

For situations in which erythromycin is contraindicated or cannot be tolerated, trimethoprim-sulfamethoxazole has been recommended, although there are no data regarding its efficacy.[1]

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Exclusion

Cases should be excluded from day care, school or other settings where there are susceptible individuals for 3 weeks from the onset of paroxysmal cough or until they have stopped coughing or until they have received 5 days of the 10-day course of erythromycin (whichever occurs first).

Suspect cases should be excluded from day care, school or similar settings until they can be evaluated with regard to etiology and potential transmission to susceptible people. Suspect cases may return to school or other settings once assessment is completed and any necessary measures are instituted. Suspect cases should not return to day care unless the diagnosis of pertussis is excluded or until they have met the same conditions required of cases.

Household or similarly close contacts of confirmed cases should be excluded from day care (or be cohorted with other contacts) for 14 days or until they have been on appropriate antibiotics for at least 5 days. It is impractical and of limited effectiveness to try to exclude contacts from school, because there are likely to be other unrecognized sources of infection.

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References

  1. Statement on management of persons exposed to pertussis and pertussis outbreak control. Can Dis Wkly Rep 1990; 16: 127-130
  2. Pertussis consensus conference. Can Commun Dis Rep 1993; 19: 124-135
  3. Pertussis surveillance: United States, 1986-1988. MMWR 1990; 39: 57-66
  4. American Academy of Pediatrics Committee on Infectious Diseases: The Redbook: Report of the Committee on Infectious Diseases, 21st ed, American Academy of Pediatrics, Elk Grove Village, Ill, 1988: 315-325
  5. Long SS, Welkon CJ, Clark JL: Widespread silent transmission of pertussis in families: antibody correlates of infection and symptomatology. J Infect Dis 1990; 161: 480-486
  6. Halperin SA, Bortolussi R, MacLean D et al: Persistence of pertussis in an immunized population: results of the Nova Scotia Enhanced Pertussis Surveillance Program. J Pediatr 1989; 115: 686-693
  7. Pertussis incidence in Canada. Can Dis Wkly Rep 1985; 11: 33-35
  8. Halperin S: Office diagnosis of pertussis. Can J Infect Dis 1992; 3: 221-222
  9. Halperin SA, Bortolussi R, Wort AJ: Evaluation of culture immunofluorescence and serology for the diagnosis of pertussis. J Clin Microbiol 1989; 27: 752-757
  10. Ewanowich CA, Chui LWL, Paranchych MG et al: Major outbreak of pertussis in northern Alberta, Canada: analysis of discrepant direct fluorescent-antibody and culture results by using polymerase chain reaction methodology. J Clin Microbiol 1993; 31: 1715-1725
  11. Nkowane BM, Wassilak SGF, McKee PA et al: Pertussis epidemic in Oklahoma: difficulties in preventing transmission. Am J Dis Child 1986; 140: 433-437
  12. Lambert HP: The carrier state: Bordetella pertussis. J Antimicrob Chemother 1986; 18 (suppl A): 13-16
  13. Steketee RW, Wassilak SGF, Adkins WN et al: Evidence for a high attack rate and efficacy of erythromycin prophylaxis in a facility for the developmentally disabled. J Infect Dis 1988; 157: 434-440
  14. Biellik RJ, Patriarca PA, Mullen JR et al: Risk factors for community- and household-acquired pertussis during a large-scale outbreak in central Wisconsin. J Infect Dis 1988; 157: 1134-1141
  15. Fisher MC, Long SS, McGowan KL et al: Outbreak of pertussis in a residential facility for handicapped people. J Pediatr 1989; 114: 934-939
  16. Muller AS, Leeuwenburg J, Pratt DS: Pertussis: epidemiology and control. Bull World Health Organ 1986; 64: 321-331
  17. Bass JW: Erythromycin for treatment and prevention of pertussis. Pediatr Infect Dis J 1986; 5: 154-157

Disclaimer

This guideline is for reference and education only and is not intended to be a substitute for the advice of an appropriate health care professional or for independent research and judgement. The CMA relies on the source of the CPG to provide updates and to notify us if the guideline becomes outdated. The CMA assumes no responsibility or liability arising from any outdated information or from any error in or omission from the guideline or from the use of any information contained in it.
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