Whooping Cough

Dr. Parag Chauhan

Introduction

  • Whooping cough, also known as pertussis, is an acute and highly contagious bacterial infection.

  • It primarily affects the respiratory tract.

  • The disease is characterized by prolonged, severe bouts of coughing.

  • Each coughing episode is often followed by a high-pitched inspiratory “whoop”, especially in children.

  • Infants and young children are the most commonly affected age group.

  • Despite the availability of effective vaccines, whooping cough continues to occur worldwide.

  • It remains a major public health problem, particularly in:

    • Infants

    • Unimmunized or partially immunized children

    • Individuals with waning immunity

  • The disease is associated with significant morbidity.

  • Mortality is highest in neonates, especially in severe or untreated cases.

  • Early diagnosis, timely treatment, and complete immunization are essential to reduce disease burden.

Etiological Agent

Whooping cough is caused by Bordetella pertussis, which has the following characteristics:

  • Small, Gram-negative coccobacillus

  • Strict aerobe

  • Non-motile, non-spore forming

  • Encapsulated

  • Extremely fastidious organism

Virulence Factors

The pathogenicity of B. pertussis is due to multiple toxins and adhesins:

  • Pertussis toxin (PT) – causes lymphocytosis, inhibits phagocytosis, and alters immune response

  • Adenylate cyclase toxin – increases intracellular cAMP, impairing neutrophil and macrophage function

  • Tracheal cytotoxin – damages ciliated epithelial cells

  • Filamentous hemagglutinin (FHA) – helps bacterial adherence

  • Fimbriae and pertactin – assist attachment to respiratory epithelium

 

Epidemiology

  • Occurs worldwide, both in developed and developing countries

  • Infants below 1 year of age are at highest risk

  • Adolescents and adults act as reservoirs of infection

  • Seasonal variation: more common in late summer and autumn

  • Immunity after infection or vaccination is not lifelong

 

Mode of Transmission

  • Spread by respiratory droplets during:

    • Coughing

    • Sneezing

    • Close personal contact

  • Highly infectious during the catarrhal stage

  • Secondary attack rate is very high in households

 

Incubation Period

  • Usually 7–10 days

  • Range: 5–21 days

 

Pathogenesis

  1. Bordetella pertussis enters via the respiratory tract

  2. Bacteria attach to ciliated epithelial cells of the trachea and bronchi

  3. Toxins cause:

    • Destruction of cilia

    • Inhibition of mucus clearance

    • Accumulation of thick mucus

  4. Airways become partially obstructed

  5. Persistent stimulation of cough receptors leads to paroxysmal coughing

Clinical Features

The disease progresses through three classical stages:

1. Catarrhal Stage (1–2 Weeks)

  • Resembles a common upper respiratory tract infection

  • Symptoms include:

    • Mild fever

    • Coryza (runny nose)

    • Sneezing

    • Mild, irritating cough

  • Maximum infectivity occurs in this stage

  • Diagnosis is difficult due to non-specific symptoms

2. Paroxysmal Stage (2–6 Weeks)

  • Hallmark stage of pertussis

  • Features:

    • Repeated, violent coughing fits (paroxysms)

    • Each episode consists of 5–15 coughs

    • Followed by a loud inspiratory “whoop”

    • Post-tussive vomiting

    • Cyanosis during coughing

  • In infants:

    • Whoop may be absent

    • Apnea and choking episodes are common

3. Convalescent Stage (Weeks to Months)

  • Gradual decrease in frequency and severity of cough

  • Recovery is slow

  • Cough may recur with secondary respiratory infections

 

Laboratory Diagnosis

1. Specimen Collection

Specimen of Choice

  • Nasopharyngeal swab or nasopharyngeal aspirate

  • Throat swabs are not recommended due to low yield

Reason

  • Bordetella pertussis adheres firmly to the ciliated epithelium of the nasopharynx

Collection Technique

  • Use a Dacron or calcium alginate swab

  • Avoid cotton swabs (contain fatty acids toxic to bacteria)

  • Insert swab gently through nostril to posterior nasopharynx

  • Collect specimen during early (catarrhal or early paroxysmal stage) for best results

2. Microscopic Examination

Gram Staining

  • Shows:

    • Small, Gram-negative coccobacilli

  • Usually present singly or in pairs

 Limitation

  • Low sensitivity and specificity

  • Cannot be relied upon for definitive diagnosis

3. Culture (Gold Standard)

Importance

  • Confirms diagnosis

  • Useful for epidemiological studies and antibiotic sensitivity testing

Culture Media

  1. Bordet–Gengou Agar

    • Potato-based medium

    • Contains blood and glycerol

  2. Regan–Lowe Medium

    • Charcoal-based medium

    • More commonly used today

    • Inhibits toxic substances and improves bacterial survival

Incubation

  • Temperature: 35–37°C

  • Atmosphere: Moist aerobic conditions

  • Duration: 3–7 days (sometimes up to 10 days)

Colony Characteristics

  • Small, smooth, glistening colonies

  • Described as “mercury drop” appearance

 Limitations

  • Sensitivity decreases after:

    • 2 weeks of illness

    • Prior antibiotic therapy

  • Time-consuming

4. Molecular Diagnosis (PCR)

Polymerase Chain Reaction (PCR)

  • Detects specific DNA sequences of B. pertussis

  • Most sensitive and rapid diagnostic method

Advantages

  • High sensitivity and specificity

  • Results available within hours

  • Useful even after antibiotic initiation

  • Preferred test in modern laboratories

Best Time

  • Catarrhal and early paroxysmal stages

5. Serological Tests

Antibody Detection

  • Measures antibodies against:

    • Pertussis toxin

    • Filamentous hemagglutinin

Methods

  • Enzyme-linked immunosorbent assay (ELISA)

Clinical Use

  • Helpful in:

    • Adolescents and adults

    • Late stages of disease

  • Not useful in early infection

 Limitation

  • Interpretation difficult in vaccinated individuals

6. Hematological Findings

Complete Blood Count (CBC)

  • Marked absolute lymphocytosis is characteristic

  • Total leukocyte count may reach 20,000–50,000/µL

Mechanism

  • Caused by pertussis toxin, which inhibits lymphocyte migration from blood to tissues

 Important Exam Point:
Lymphocytosis in a coughing child strongly suggests pertussis.

 

Treatment

Antibiotic Therapy

  • Most effective in early (catarrhal) stage

  • Drugs of choice:

    • Azithromycin

    • Clarithromycin

    • Erythromycin

  • Alternatives: Trimethoprim-sulfamethoxazole

Supportive Management

  • Oxygen therapy

  • Adequate nutrition and hydration

  • Monitoring for apnea in infants

  • Isolation for at least 5 days after starting antibiotics

 

Complications

More common in infants and unvaccinated children:

  • Pneumonia (most common cause of death)

  • Apnea

  • Seizures

  • Encephalopathy

  • Subconjunctival hemorrhage

  • Rectal prolapse

  • Failure to thrive

 

Prevention

Immunization

  • Most effective preventive measure

  • Given as:

    • DTaP in infants and children

    • Tdap booster in adolescents and adults

  • Part of national immunization programs

Chemoprophylaxis

  • Macrolide antibiotics for close contacts

 

Public Health Importance

  • Pertussis remains a re-emerging infection

  • Incomplete vaccination and waning immunity contribute to outbreaks

  • Early diagnosis, vaccination, and surveillance are essential for control

 

MCQs

1. Whooping cough is also known as:

A. Diphtheria
B. Bronchiolitis
C. Pertussis
D. Tuberculosis
Answer: C

2. Whooping cough is caused by:

A. Streptococcus pneumoniae
B. Haemophilus influenzae
C. Bordetella pertussis
D. Corynebacterium diphtheriae
Answer: C

3. Bordetella pertussis is:

A. Gram-positive bacillus
B. Gram-negative coccobacillus
C. Gram-positive cocci
D. Acid-fast bacillus
Answer: B

4. The disease mainly affects:

A. Elderly
B. Neonates and infants
C. Only adults
D. Pregnant women
Answer: B

5. Mode of transmission of pertussis is:

A. Feco-oral
B. Vector-borne
C. Respiratory droplets
D. Blood transfusion
Answer: C

6. Incubation period of whooping cough is usually:

A. 1–3 days
B. 3–5 days
C. 7–10 days
D. 30 days
Answer: C

7. Which stage of pertussis is most infectious?

A. Convalescent stage
B. Paroxysmal stage
C. Catarrhal stage
D. Recovery stage
Answer: C

8. The hallmark feature of whooping cough is:

A. Rash
B. Fever
C. Inspiratory whoop
D. Diarrhea
Answer: C

9. Severe coughing spells occur in which stage?

A. Catarrhal
B. Paroxysmal
C. Convalescent
D. Incubation
Answer: B

10. Post-tussive vomiting is seen in:

A. Catarrhal stage
B. Paroxysmal stage
C. Incubation stage
D. Latent stage
Answer: B

11. In infants, whooping cough may present with:

A. Diarrhea
B. Apnea
C. Skin lesions
D. Joint pain
Answer: B

12. The organism attaches to which cells?

A. Alveolar macrophages
B. Squamous cells
C. Ciliated epithelial cells
D. Endothelial cells
Answer: C

13. Which toxin causes lymphocytosis?

A. Endotoxin
B. Exotoxin A
C. Pertussis toxin
D. Hemolysin
Answer: C

14. Pertussis is mainly a:

A. Invasive disease
B. Toxin-mediated disease
C. Blood-borne disease
D. Zoonotic disease
Answer: B

15. Specimen of choice for diagnosis is:

A. Throat swab
B. Sputum
C. Nasopharyngeal swab
D. Blood
Answer: C

16. Best time to collect specimen is during:

A. Late convalescent stage
B. Early catarrhal stage
C. After 6 weeks
D. After antibiotics
Answer: B

17. Gold standard diagnostic method is:

A. Gram stain
B. PCR
C. Culture
D. Serology
Answer: C

18. Culture medium for Bordetella pertussis is:

A. Blood agar
B. Chocolate agar
C. Bordet–Gengou agar
D. MacConkey agar
Answer: C

19. Regan–Lowe medium contains:

A. Serum
B. Charcoal
C. Egg yolk
D. Tellurite
Answer: B

20. Colony appearance of B. pertussis is described as:

A. Rough colonies
B. Mucoid colonies
C. Mercury drop colonies
D. Hemolytic colonies
Answer: C

21. Most sensitive diagnostic test is:

A. Culture
B. PCR
C. Gram stain
D. CBC
Answer: B

22. PCR is useful because it is:

A. Cheap
B. Slow
C. Highly sensitive and rapid
D. Non-specific
Answer: C

23. CBC in pertussis shows:

A. Neutrophilia
B. Eosinophilia
C. Lymphocytosis
D. Thrombocytopenia
Answer: C

24. Lymphocytosis is caused due to:

A. Bone marrow failure
B. Pertussis toxin
C. Secondary infection
D. Antibiotics
Answer: B

25. Drug of choice for treatment is:

A. Penicillin
B. Cephalosporin
C. Macrolide
D. Aminoglycoside
Answer: C

26. Most effective stage for antibiotic therapy is:

A. Convalescent
B. Late paroxysmal
C. Early catarrhal
D. Recovery
Answer: C

27. Which antibiotic is commonly used?

A. Ciprofloxacin
B. Azithromycin
C. Vancomycin
D. Doxycycline
Answer: B

28. Most common complication of pertussis is:

A. Otitis media
B. Pneumonia
C. Arthritis
D. Nephritis
Answer: B

29. Severe complication seen in infants includes:

A. Hypertension
B. Apnea
C. Jaundice
D. Rash
Answer: B

30. Whooping cough vaccine is given as part of:

A. BCG
B. OPV
C. DPT
D. Measles
Answer: C

31. Pertussis vaccine is a:

A. Live attenuated vaccine
B. Killed vaccine
C. Toxoid
D. Recombinant vaccine
Answer: B

32. Acellular pertussis vaccine contains:

A. Whole bacteria
B. Only endotoxin
C. Purified antigens
D. Spores
Answer: C

33. Booster dose is required because immunity is:

A. Lifelong
B. Permanent
C. Short-lived
D. Genetic
Answer: C

34. Adolescents and adults act as:

A. Dead-end hosts
B. Reservoirs of infection
C. Immune carriers
D. Resistant hosts
Answer: B

35. Whooping sound is produced due to:

A. Bronchospasm
B. Sudden inspiration after coughing
C. Vocal cord damage
D. Lung collapse
Answer: B

36. Duration of paroxysmal stage is about:

A. 2–3 days
B. 1 week
C. 2–6 weeks
D. 6 months
Answer: C

37. The disease is most dangerous in:

A. Adults
B. Elderly
C. Infants
D. Teenagers
Answer: C

38. Throat swab is not preferred because:

A. Difficult to collect
B. Painful
C. Low bacterial yield
D. Expensive
Answer: C

39. Serology is useful mainly in:

A. Early disease
B. Neonates
C. Late disease in adults
D. Vaccinated infants
Answer: C

40. Culture sensitivity decreases after:

A. 24 hours
B. 3 days
C. 2 weeks
D. 6 months
Answer: C

41. The organism is:

A. Anaerobic
B. Facultative anaerobe
C. Strict aerobe
D. Microaerophile
Answer: C

42. Bordetella pertussis is:

A. Spore forming
B. Motile
C. Non-motile
D. Flagellated
Answer: C

43. Disease control mainly depends on:

A. Isolation only
B. Antibiotics only
C. Vaccination
D. Nutrition
Answer: C

44. Chemoprophylaxis is recommended for:

A. General population
B. Close contacts
C. Recovered patients
D. Vaccinated individuals
Answer: B

45. Most characteristic lab finding in a coughing child is:

A. Anemia
B. Neutropenia
C. Lymphocytosis
D. Thrombocytosis
Answer: C

46. Whooping cough primarily affects which system?

A. Digestive
B. Nervous
C. Respiratory
D. Urinary
Answer: C

47. Disease spreads fastest in:

A. Hospitals
B. Households
C. Open areas
D. Laboratories
Answer: B

48. Which stage shows gradual recovery?

A. Catarrhal
B. Paroxysmal
C. Convalescent
D. Incubation
Answer: C

49. Death in pertussis is usually due to:

A. Dehydration
B. Pneumonia
C. Renal failure
D. Liver failure
Answer: B

50. Best preventive strategy for pertussis is:

A. Early diagnosis
B. Antibiotic therapy
C. Vaccination
D. Isolation
Answer: C