Whooping Cough (Pertussis)

Pertussis (whooping cough) is caused by Bordetella pertussis, a fastidious, aerobic, gram-negative bacterium that colonizes the ciliated epithelium of the human respiratory tract; humans are its only reservoir.^[1][2] It is genuinely among the most contagious diseases pharmacists will encounter — studies report an 80% secondary attack rate among susceptible household contacts — spread by inhalation of infectious respiratory particles, direct contact of mucosal surfaces with infectious secretions, and, rarely, contaminated fomites.^[1] The incubation period is 5 to 10 days, with a range of 4 to 21 days.^[1]

The disease produces its own toxins (chiefly pertussis toxin, along with adenylate cyclase toxin and tracheal cytotoxin) that disrupt mucociliary clearance and immune signalling, producing the disease's signature prolonged, paroxysmal cough rather than invasive bloodstream infection.^[2] Illness classically unfolds across three named stages — catarrhal, paroxysmal, and convalescent — covered in full in Recognize the Condition, but two facts drive essentially everything a pharmacist needs to get right about this disease. First, a young infant, especially one under 3 months of age, may never show the classic whoop at all: the presentation can be apnea alone, and this age group carries by far the highest risk of hospitalization and death.^[1][3] Second, this is one of the few vaccine-preventable diseases where the single highest-value pharmacist action is not a treatment decision at all — it is making sure a pregnant patient receives Tdap in the early third trimester of every pregnancy, and that the people who will be holding that baby have had their own lifetime adult dose.^[4][5]

Pertussis is endemic and cyclical in Canada, with case peaks at 2- to 5-year intervals, and it has been a nationally notifiable disease since 1924.^[1] Vaccination drove incidence down from an average of 156 cases per 100,000 population in the five years before any vaccine was available (1938-1942) to a low of 2.3 per 100,000 between 2019 and 2023 — but case counts rose again in 2024 and 2025 by more than the usual cyclic pattern would predict, a genuinely current reminder that pertussis is not a solved problem in Canada and that routine counselling on this vaccine still matters at every opportunity.^[1]

Three classic stages

Gram stain of Bordetella pertussis, the small gram-negative coccobacillus responsible for whooping cough. (CDC Public Health Image Library #2121, 1979 — public domain, Wikimedia Commons)

The presentation that is genuinely easy to miss: young infants

Adolescents and adults: often milder, often unrecognized, and the actual source of most infant exposures

Pertussis in adolescents and adults ranges from asymptomatic infection to a very prolonged, debilitating cough, frequently without the whoop or post-tussive vomiting that make the diagnosis obvious in a child.^[1][2] This matters enormously in practice: pertussis is a common and often unrecognized cause of a cough persisting more than 2 weeks in this age group, with one estimate putting the prevalence of pertussis among adults presenting with a prolonged cough at 12% to 32%.^[2] Because waning vaccine- and infection-derived immunity means most transmission to vulnerable infants comes from parents, siblings, and other close contacts with exactly this kind of unrecognized cough, a pharmacist who takes a "cough for over two weeks" complaint seriously — and asks about any young infant in the household — is doing genuine, concrete prevention work.^[4]

Differential diagnosis for a prolonged cough

Consider pertussis alongside these more familiar causes whenever a cough has lasted 2 weeks or more, particularly with paroxysms, a whoop, or post-tussive vomiting:

• Post-viral / post-infectious cough following an ordinary upper respiratory infection — usually improving, not paroxysmal, and without a whoop.
• Bordetella parapertussis infection — produces a similar but generally milder pertussis-like illness.^[2]
• Undiagnosed or poorly controlled asthma/reactive airway disease, particularly with a nocturnal or exertional pattern.
• Gastroesophageal reflux-associated cough, especially in infants.
• ACE-inhibitor-associated cough in an adult on that drug class.
• Allergic rhinitis with postnasal drip.
• An inhaled foreign body in a young child with a sudden-onset cough and no preceding cold-like prodrome.

The CDC/WHO clinical case definitions used to guide suspicion require a cough of any duration plus at least one of paroxysmal coughing, inspiratory whoop, post-tussive emesis, or apnea (with contact with a laboratory-confirmed case), or at least 2 weeks of coughing plus one of those same features; both are sensitive but not specific, which is exactly why laboratory confirmation matters (see Assessment & Diagnosis).^[2]

• Age under 6 months, and especially under 3 months — too young to have completed the primary vaccine series, and the group with by far the highest risk of hospitalization, complications, and death.^[1][4]
• Being unimmunized or under-immunized at any age.^[1]
• Waning immunity in adolescents and adults — vaccine- and infection-derived protection both decline over time, which is why this age group so often becomes the (frequently unrecognized) source of infant exposures.^[4]
• Close/household contact with a person who has pertussis: secondary attack rates among susceptible household contacts run as high as 80%.^[1]
• Missed or delayed routine booster doses, particularly the 4-to-6-year and 14-to-16-year boosters — protection is known to decline progressively after the second (4-to-6-year) booster dose.^[1][4]
• Pregnancy without a current-pregnancy Tdap dose — not a risk factor for more severe maternal disease specifically, but the single most important modifiable risk factor for the infant's own risk after birth.^[5]
• Chronic respiratory disease or immunocompromise, which raise the risk of a more severe course at any age.^[2]
• Healthcare workers and child care workers without a documented adult-life pertussis-containing dose, given occupational exposure to both cases and vulnerable infants.^[4]
• International travel to or residence in an area with lower vaccine coverage or ongoing circulation.

When to suspect pertussis

Suspect pertussis in anyone with a cough of 2 or more weeks' duration, paroxysmal coughing episodes, post-tussive vomiting, an inspiratory whoop, or — specifically in infants — apnea with or without cyanosis, particularly with a known exposure.^[1] Neither the CDC nor WHO clinical case definition is specific on its own; laboratory confirmation genuinely changes management, particularly around contact prophylaxis and public-health reporting, and should be pursued rather than treated purely as a formality.^[2]

Confirmatory testing

In practical terms: PCR and culture are both most useful in the first 2-3 weeks of cough, while serology becomes more useful only after that window, once bacterial DNA is less reliably detectable and antibody has had time to rise — an important, genuine timing limitation to set expectations around rather than a flaw unique to any one test.^[2]

Supportive laboratory findings

A complete blood count showing leukocytosis with absolute lymphocytosis supports the diagnosis, especially in young children; in infants under 3 months with a compatible presentation, a white blood cell count over 20,000/µL with more than 50% lymphocytes is highly suggestive. In severe infant cases, counts can exceed 100,000/µL, and marked lymphocytosis has been specifically associated with pulmonary hypertension and higher mortality — a genuine red flag in a hospitalized infant, not just a lab curiosity.^[2]

Reporting

Pertussis has been a nationally notifiable disease in Canada since 1924. Report suspected cases meeting the case definition to the local public health unit promptly rather than waiting on laboratory confirmation, since timely reporting is what drives contact tracing and post-exposure prophylaxis for the people actually at risk from this specific case.^[1]

• Recognize pertussis even when it doesn't look classic — especially the infant who presents with apnea alone, and the adult with "just a cough that won't go away."
• Start antibiotic treatment as early as possible to reduce transmission, while counselling accurately that treatment mainly limits spread rather than dramatically shortening an already-established paroxysmal-phase cough.
• Identify and offer post-exposure prophylaxis promptly to household and other high-risk contacts, especially infants, pregnant people, and the immunocompromised.
• Give clear isolation guidance that genuinely limits ongoing transmission, and confirm the case has been reported to public health.
• Escalate red-flag presentations — infant apnea above all — immediately rather than managing them as routine cough.
• Deliver accurate, current counselling on the Tdap schedule across the lifespan, with genuine emphasis on Tdap in every pregnancy and the complementary cocooning of close infant contacts.
• Set realistic, honest expectations about the natural course of the cough and the limits of antibiotic therapy once paroxysms have started.

Post-exposure prophylaxis (PEP) — who, and when

Offer the same macrolide regimens used for treatment (azithromycin is typical) as post-exposure prophylaxis to:^[2]

• All household contacts of a confirmed or strongly suspected case.
• Anyone at high risk for severe disease who has been exposed — infants under 12 months, pregnant people, immunocompromised individuals, and people with significant underlying respiratory or other chronic conditions.
• Close contacts of any of the above high-risk individuals, including healthcare team members with relevant exposure.

PEP is most effective when started within 21 days of the index case's cough onset — beyond that window its value is much less clear, and the practical priority shifts to symptom monitoring and prompt treatment if illness develops.^[2] Alongside PEP, verify the immunization status of exposed contacts (especially children) and give any recommended pertussis-containing vaccine doses that are due, since this is also a genuine opportunity to close an immunity gap going forward, independent of the current exposure.^[1]

Isolation — the other lever that actually limits spread

Confirmed or suspected case isolate from young children and infants until at least 5 days of appropriate antibiotic treatment have been completed — patients are no longer considered contagious at that point.^[1] Suspected case not receiving antibiotics isolate (stay home from school, work, and other public settings, and avoid close contact with others, especially anyone at risk of severe disease) for 3 weeks after paroxysmal cough onset, or until the cough ends — whichever comes first.^[1] Reinforce mask/respirator use when around others, covering coughs, and hand hygiene throughout.^[1]

The Tdap vaccination schedule — the highest-leverage prevention action in this chapter

^[4][1]

Tdap in pregnancy — this chapter's centerpiece counselling point

NACI recommends that every pregnant person receive one dose of Tdap in every pregnancy, regardless of past immunization history, ideally between 27 and 32 weeks of gestation.^[4][5] The rationale is entirely about the newborn: maternal vaccination in the third trimester allows efficient transplacental transfer of protective antibody to the fetus, providing the infant with passive protection during the first two months of life — precisely the highest-risk window, before the infant's own primary series can even begin at 2 months.^[4] This is not a marginal effect: Tdap immunization in pregnancy is estimated to protect approximately 9 of 10 infants under 3 months of age against pertussis.^[4] If 27-32 weeks is missed, vaccination remains worthwhile anytime from 13 weeks up to delivery — earlier administration (13-26 weeks) is a reasonable alternative when there is an increased risk of preterm delivery or a travel-related time constraint, and even late-pregnancy administration retains partial protective value, though ideally at least 4 weeks before delivery allows the fullest antibody transfer.^[4][5] A patient who already had Tdap in a previous pregnancy still needs it again in this one — protection does not carry over between pregnancies, and this is one of the most common, avoidable gaps in counselling.^[4]

Cocooning — vaccinating the people who will hold the baby

"Cocooning" is the practice of vaccinating close household members and other caregivers of a newborn — partners, grandparents, siblings old enough for their own doses, and regular child care providers — so that the people actually in close contact with the infant are not themselves a transmission source. Canada's working version of this recommendation, per the Canadian Immunization Guide, is specific and actionable: any adult who has not yet received a pertussis-containing vaccine dose in adulthood, and who anticipates regular contact with an infant, should receive a dose of Tdap — ideally at least 2 weeks before that contact begins.^[4] Parents and siblings are specifically named as an important source of pertussis transmission to young infants, which is exactly the transmission chain cocooning is meant to interrupt.^[4]

Be honest about where cocooning fits. It is a genuine, worthwhile complement to maternal Tdap — but not a substitute for it, and not equally effective on its own. A Canadian parent-facing summary states this plainly: young babies can also be protected if everyone around them has been appropriately vaccinated, but that does not seem to protect them as well as vaccinating the pregnant parent directly.^[3] Practically, this means: counsel every pregnant patient on their own Tdap dose first and as the priority action, and use the same visit (or any visit with an expectant or new parent) to ask whether other close contacts — the other parent, grandparents, an older sibling due for their own booster — have ever had an adult dose, and offer it if not.

Comfort measures during active illness

• Small, frequent feeds/fluids rather than large ones, particularly in infants and young children — post-tussive vomiting is common, and smaller volumes are easier to tolerate and reduce dehydration risk.^[3]
• A calm, unhurried environment; sudden triggers, crying, and vigorous activity can provoke coughing paroxysms in some patients.
• Avoid exposure to smoke, strong fumes, or other airway irritants that can trigger coughing fits.
• Elevate the head of the bed for older children and adults if this is comfortable and improves rest, though evidence for this specific measure is limited.
• Prepare caregivers explicitly for how long the cough can last (up to 6-12 weeks total, sometimes longer) so a slow but genuine recovery is not mistaken for treatment failure.^[3]

Isolation and household management

• Isolate a confirmed/suspected case from young children and infants until at least 5 days of appropriate antibiotic treatment are complete; without treatment, isolate for 3 weeks from paroxysmal-cough onset or until the cough resolves, whichever comes first.^[1]
• Use a well-fitting mask/respirator around others when isolation cannot be fully maintained, cover coughs and sneezes, and reinforce hand hygiene for the whole household.^[1]
• Verify the immunization status of every household and close contact, and offer catch-up or PEP dosing as indicated (see Choose Initial Treatment) — this is where a pharmacist's counselling has real, concrete outbreak-control value, not just individual-patient value.^[1]
• Confirm the case has actually been reported to the local public health unit — this drives the contact-management and PEP response for everyone genuinely at risk from this specific exposure, and should not be assumed to have happened automatically.^[1]

What does not help

• Over-the-counter cough and cold preparations, antihistamines, and cough suppressants have not shown consistent benefit for pertussis-related cough and are not routinely recommended — a genuinely useful thing to say plainly to a frustrated caregiver rather than reaching for something just to offer them relief.^[2]
• Bronchodilators and corticosteroids likewise lack demonstrated benefit for pertussis cough in the absence of a separate reason (e.g., known reactive airway disease) to use them.^[2]

Infants under 6 months, and especially under 3 months

This is the population the entire chapter is built around. Presentation is frequently atypical — apnea with or without cyanosis may be the only sign, without a classic whoop or post-tussive vomiting.^[1][4] About 30% of infected infants under 1 year are hospitalized, and nearly all Canadian pertussis deaths occur in unimmunized or underimmunized infants under 6 months.^[1][4] Hospitalized infants need close monitoring for apnea, hypoxia, dehydration, and feeding difficulty; in extreme cases with marked leukocytosis and pulmonary hypertension, specialist-level supportive care (up to exchange transfusion or extracorporeal membrane oxygenation in refractory cases) may be required — this is specialist/ICU territory, not community management, but pharmacists should recognize how serious the severe end of this presentation can be when counselling a worried parent.^[2] The single most effective protection for this age group before their own vaccine series begins is passive antibody from maternal Tdap in pregnancy (see Choose Initial Treatment) plus cocooning of close contacts.

Pregnancy — the centerpiece prevention decision

NACI's recommendation reached its current form in 2018, after review of accumulating international effectiveness and safety data: Tdap should be offered to every pregnant person in every pregnancy, regardless of immunization history, ideally between 27 and 32 weeks of gestation.^[5] This replaced an earlier (2013) recommendation that limited routine use to outbreak settings or unimmunized adults, once evidence showed that routine maternal immunization is both safer and more effective at preventing severe infant outcomes than an outbreak-triggered approach, which is logistically harder to execute and reaches fewer at-risk infants in time.^[5] Maternal Tdap has a strong safety record in pregnancy, and peak maternal antibody levels are reached about 4 weeks after vaccination, with optimal placental transfer occurring in the third trimester — which is why the 27-32-week window balances strong safety data with enough time for a full antibody response before typical term delivery.^[4] Vaccination earlier (13-26 weeks) is a reasonable alternative when there is an elevated risk of preterm delivery or a travel-related time constraint, since it still allows meaningful antibody transfer for infants born before 37 weeks; vaccination anytime up to delivery, even close to term, still offers the infant some partial protection, though with less time for the mother's own antibody response to fully develop.^[4] A patient should be offered Tdap in this pregnancy even if she received it in a previous one — protection is not assumed to carry forward.^[4] If Tdap was missed antenatally, postpartum vaccination before hospital discharge is still worthwhile, though it will not provide the newborn with passive antibody the way antenatal dosing does.

Cocooning: household and caregiver contacts of a newborn

See Choose Initial Treatment for the specific Canadian recommendation and dosing timing. The genuinely important nuance for counselling is honesty about the evidence: cocooning is a real, worthwhile complement to maternal vaccination, but current Canadian patient-facing guidance is explicit that it does not appear to protect an infant as well as vaccinating the pregnant parent does.^[3] Practical priority order: (1) confirm the pregnant patient's own current-pregnancy Tdap status first, (2) then ask about the other parent's and any regular caregivers' adult-life Tdap history, and (3) offer the dose to anyone who has not yet had one, ideally at least 2 weeks before their expected close contact with the newborn begins.^[4]

Premature infants

Premature infants in stable clinical condition should be vaccinated at the same chronological age and on the same schedule as full-term infants — prematurity is not a reason to delay the primary series. Premature infants, particularly those under 1,500 g at birth, are at higher risk of apnea and bradycardia following vaccination, so hospitalized premature infants should have continuous cardiac and respiratory monitoring for 48 hours after their first dose.

Immunocompromised patients

Pertussis-containing combination vaccines are not live vaccines and may be administered to immunocompromised patients; consultation with the patient's attending physician can help guide timing and expectations around immune response in complex cases.

Renal and hepatic impairment

No dose adjustment is required for any pertussis-containing vaccine. Among the antimicrobial options, TMP-SMX requires dose adjustment (or avoidance) in significant renal impairment given reduced clearance, and macrolide dosing should be used cautiously with relevant hepatic impairment given hepatic metabolism; azithromycin is generally the best-tolerated option to start from in either scenario, with pharmacist input on adjustment as needed.

• Set the expectation up front that recovery is gradual — paroxysms typically ease over 1-6 weeks (up to 10) and residual cough can linger for weeks to months, so "still coughing" 3-4 weeks after starting antibiotics is an expected course, not necessarily treatment failure.^[1][2]
• Reassess any infant closely and with a low threshold to escalate — a change in feeding, activity, colour, or any new apnea episode warrants prompt medical reassessment rather than a "keep watching at home" approach.^[1]
• Confirm the full antibiotic course was completed, and specifically confirm the patient/caregiver understands isolation can end after 5 days of treatment (or continues for 3 weeks from paroxysmal-cough onset if untreated).^[1]
• Follow up on whether household/close contacts actually received PEP and had their vaccination status reviewed and updated — not just that it was discussed at the original visit.^[1]
• Confirm the case was actually reported to public health, rather than assuming it happened automatically.^[1]
• For a pregnant patient, confirm the current-pregnancy Tdap dose was actually given (not just recommended), and document it clearly for the postpartum/newborn record.^[5]

1. New or worsening apnea, cyanosis, poor feeding, or lethargy in an infant at any point in the illness: this is an urgent/emergency reassessment, not an antibiotic-adjustment decision.
2. Cough is not meaningfully improving well into the convalescent timeframe (well beyond 6-10 weeks): reconsider the diagnosis — a secondary bacterial complication (e.g., pneumonia), an alternative or coexisting cause of chronic cough (see Recognize the Condition's differential), or, rarely, reinfection.
3. Symptoms/signs of a complication develop mid-course — new fever with focal chest findings (possible pneumonia), a new seizure or altered mental status (possible encephalopathy), or severe dehydration in an infant: escalate for medical assessment rather than treating as an expected part of the illness.
4. A patient cannot tolerate or is allergic to macrolides: switch to TMP-SMX if age 2 months or older and not near-term pregnant; involve the prescriber for anyone outside those parameters.
5. PEP was not started within the usual 21-day window after an exposure: still consider case-by-case, particularly for a high-risk contact (infant, pregnant person, immunocompromised), and shift emphasis toward close symptom monitoring and a low threshold for prompt testing/treatment if illness develops.
6. A pregnant patient or new parent is hesitant about Tdap: address specific concerns directly (the strong third-trimester safety data, and the concrete 9-in-10 infant protection figure) rather than deferring the conversation — this is genuinely time-sensitive given the 27-32-week window.

• Dismissing brief apnea episodes in a young infant because there is no classic whooping cough — apnea alone can be the entire presentation in this age group, and it is exactly the presentation most likely to be missed.^[1][4]
• Expecting antibiotics to dramatically shorten an already-established paroxysmal-phase cough — set the expectation up front that treatment mainly reduces transmission, not the cough's own duration, to avoid a frustrated "the antibiotics didn't work" follow-up visit.^[2]
• Using erythromycin or clarithromycin as first choice in a neonate — azithromycin is preferred at this age; erythromycin carries a specific association with infantile hypertrophic pyloric stenosis in young infants, and clarithromycin lacks adequate safety data under 1 month.^[6]
• Using TMP-SMX in an infant under 2 months, or reaching for it near term in pregnancy, given kernicterus risk in both situations.^[2]
• Assuming a documented adolescent Tdap dose means an adult patient is fully "up to date" for life — the routine adult recommendation is a separate, single lifetime adult-life dose, distinct from the ongoing decennial Td/Tdap schedule used for tetanus/diphtheria wound prophylaxis (see the Tetanus chapter) — these are two different schedules that are easy to conflate.^[4]
• Treating cocooning as an equivalent substitute for maternal Tdap rather than a complement to it — current Canadian guidance is explicit that vaccinating everyone around a baby does not protect as well as vaccinating the pregnant parent directly.^[3]
• Not offering Tdap in the current pregnancy because the patient already had it in a previous one — NACI recommends dosing in every pregnancy regardless of history, since protection does not carry forward.^[4][5]
• Missing pertussis in the differential for an adult's "cough that won't go away," and reflexively treating it as post-viral or allergic without considering testing — pertussis is estimated to explain 12%-32% of prolonged coughs in adults presenting with this complaint.^[2]
• Reaching for OTC cough suppressants, antihistamines, or bronchodilators as reflex symptom relief for pertussis cough — none have consistent demonstrated benefit for this specific cough.^[2]
• Forgetting to confirm a suspected/confirmed case was actually reported to public health, and that household contacts actually completed PEP and vaccine catch-up rather than just having it discussed.^[1]

How to use this table: antimicrobial doses are adult/pediatric doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history, gestational age if pregnant). Vaccine timing follows the schedule in Choose Initial Treatment. Select any drug or vaccine name to open its complete Pharmasist Drug Database page.

Antimicrobial Therapy — Treatment and Post-Exposure Prophylaxis

Age-banded regimen per the 2005 CDC guideline that PHAC itself references for antimicrobial specifics. The same regimen used for treatment is used for post-exposure prophylaxis. Start as early as possible; still reasonable for up to 3 weeks after cough onset, primarily to reduce transmission.

Symptomatic Comfort Care

No drug shortens the cough itself once the paroxysmal phase is established; these support comfort only.

Not Routinely Recommended

No consistent demonstrated benefit for pertussis-related cough specifically — be direct with caregivers rather than offering these as a reflex placebo gesture.

Pertussis-Containing Vaccines — Active Immunization

See Choose Initial Treatment for the full age/situation schedule, including the pregnancy and cocooning decisions. All are 0.5 mL IM per dose.