Whooping cough (pertussis) presents as intense cough that comes in spells that can be life-threatening for small infants.
In Finland, basic vaccination against whooping cough is given as a part of the national immunization programme at the age of 3, 5 and 12 months (DTaP vaccine). Booster vaccination is given at the ages of 4 and 14 to 15 years. In adults, a booster vaccination is given at the age of 25 and to military conscripts. See Vaccinations Vaccinations.
Dangerous whooping cough occurs particularly in infants less than 3 months of age and in unvaccinated or partially vaccinated older infants. Because the protection provided by the vaccine is of short duration, whooping cough is also encountered as paroxysmal cough in school-age children and in adults.
Antimicrobial treatment using a macrolide is given to all infants with suspected whooping cough and to those older children and adults who have a confirmed diagnosis and in whom the symptoms have lasted less than 4 weeks.
Causative agent
Bordetella pertussis
Similar but milder disease can also be caused by B. parapertussis, possibly also by various viruses.
B. pertussis is extremely contagious.
Prevalence
Prevalence varies and depends on how well the population is protected by immunization.
Maternal vaccination in childhood is not sufficient to protect the neonate. In countries with high prevalence of pertussis, vaccination of pregnant women is nowadays used to protect the newborn infants.
School children: Immunity confered by vaccination lasts only 3-6 years.
Clinical picture
Incubation period 1-2 weeks
Clinical diagnosis is based on history, especially on occurrence of coughing spells.
In unvaccinated infants during the catarrhal phase (1-2 weeks) there is slight cough, red eyes and rhinitis, sometimes also mild fever.
In infants, turning blue or even respiratory arrest during an attack may be the first symptom.
During the coughing phase there are spells of coughing. In infants these may be associated with inspiratory stridor or whooping. In vaccinated school-age children and in adults, the clinical presentation is mostly atypical without whoops. The spells of coughing occur at night in particular, and often conclude with vomiting of mucus. The spells continue to occur in high frequency for 1-4 weeks and then become less frequent. They may recur during a new viral respiratory infection.
During the coughing phase the patient is afebrile. CRP and ESR are usually normal.
A school child with whooping cough is usually brought for consultation because of cough that has lasted for weeks or months. The cough is usually described as being exceptionally severe, and almost always occurring in spells. Often the patients describe the illness as a cough unlike any other they have ever had before. A cough that lasts for more than one month often is pertussis and always requires closer investigations.
Stress, cigarette smoke and changes of temperature (eating ice cream, for example) can trigger a spell of coughing. Such hyper-reactivity of the airways can last for 3-6 months, and asthma may be suspected.
Whooping cough also occurs in adults. Other persons with coughing spells are often found in the immediate surroundings.
Whooping cough may in unvaccinated infants cause strong lymphocytosis which is a sign of severe disease. The lymphocytosis is caused by a strong effect of pertussis toxin which may lead to pulmonary hypertension.
Diagnosis
In the acute phase (symptoms for less than 4 weeks), direct demonstration of pertussis bacilli in a nasopharyngeal sample by a PCR test. For PCR, a Copan or Dacron swab is used (check details from local laboratory). The sample for culture is applied on a special growth medium (charcoal/cephalexin dish). Dishes and sample pins can be ordered from microbiological laboratories.
In older children and in adults, the diagnosis is made on the basis of a serum sample, as the antibodies increase to diagnostic levels 3-4 weeks after symptoms commence.
IgG against pertussis toxin is used in serology nowadays. It should be noted that also vaccinations increase the level of these antibodies.
Serology should not be used in vaccinated children below 2 years of age or within a year after vaccination.
Negative serological findings do not exclude whooping cough, because the sensitivity of the test often is only 50-60%.
Fresh disease cases (duration of symptoms less than 4 weeks) in the surroundings of a patient who has a cough coming in spells should be sampled for PCR, in order to detect pertussis at an early stage especially in small children.
After diagnosis has been confirmed on the basis of results of tests relating to one patient or several patients, treatment decisions relating to contacts can be made on the basis of their clinical symptoms.
Infants and particularly unvaccinated children are always treated in a hospital.
The drug of choice is azithromycin 10 mg/kg/day for 5 days, for older children and for adults 500 mg on the first day and then 250 mg daily for 4 days. Roxithromycin and clarithromycin are alternatives. Amoxicillin or cephalosporins are not useful.
If there is a child under 6 months of age or a woman 36 weeks or more pregnant in the family of a pertussis patient, the entire family should be given antimicrobial prophylaxis irrespective of the symptom picture or vaccination status. Also other individuals in close contact with the family may require prophylactic measures. See local guidance for further advice.
The primary aim of treatment is to reduce infectivity and spread. In order for the treatment to affect symptoms it must be started as soon as possible after suspicion of pertussis arises. In practice, the treatment is started immediately after a sample is taken for PCR if the symptoms and the epidemiological situation suggest whooping cough.
If the patient has exhibited symptoms for over one month, treatment is not worthwhile. Repeated courses of antimicrobials are of no benefit.
The period of isolation should be 5 days from the start of antimicrobial treatment. If symptoms have lasted for more than 3 weeks, isolation is unnecessary.
Adults may protect themselves by taking dtap booster vaccination instead of a dT booster. This also provides additional protection to the youngest members of the family due to herd immunity.
References
Locht C. Will we have new pertussis vaccines? Vaccine 2018;36(36):5460-5469. [PubMed]