Whooping cough

Pathogen and transmission
Whooping cough (pertussis or 100-day cough) is caused by the bacteria Bordetella pertussis and Bordetella parapertussis. After colonising the respiratory mucosa, they form a variety of toxins, whose effects include local destruction of the infected epithelia. The pertussis toxin is formed exclusively by B. pertussis.
It is transmitted during both the catarrhal stage and the paroxysmal stage via droplets (through coughing, sneezing and speaking). Over 90 % of unprotected people exposed to it become ill. The incubation period is 7 to 20 days.

Clinical signs and symptoms
In the unspecific catarrhal stage (duration of 1-2 weeks), coughing and cold symptoms with sub-febrile temperatures develop. The subsequent paroxysmal stage (duration 4-6 weeks), is marked by a staccato cough, coughing fits with inspiratory stridor and even vomiting. The coughing fits occur more frequently at night. Infants tend more to suffer apnoea attacks rather than fits of coughing. High temperatures can be an indication of a secondary bacterial infection. In the recovery stage (duration of 6-10 weeks) the fits of coughing progressively diminish. A secondary infection or an infection long after the vaccination (partial immunity) is often characterised by a cough that persists for several weeks and a strong feeling of being generally unwell. Infections with B. parapertussis follow a similar course, but are usually shorter and less severe.

Laboratory diagnosis
Laboratory diagnostics depends on the stage of the disease. During the catarrhal stage and at the beginning of the paroxysmal stage, direct detection by the polymerase chain reaction (PCR) is the diagnostic method of choice. It is a quick and highly sensitive way to detect Bordetella pertussis and Bordetella parapertussis from swabs taken from the nasopharyngeal area.

PCR
The PCR is indicated for diseases in infants and children of pre-school age, school children, adolescents and adults up to the third week of coughing and is included in the service catalogue of statutory health insurance. In the transition to the paroxysmal stage (after approximately 2-3 weeks), antibodies are detectable.

Serology
Provided that the patient received no vaccination during the past year, IgG and IgA antibodies against the pertussis toxin (PT) can be used to determine whether the patient recently came in contact with the pathogen. With the corresponding symptoms, detecting antibodies therefore helps to diagnose whooping cough.

The assessment of the serology is based on PT-specific IgG and IgA in accordance with the recommendations of European reference laboratories.

IgG < 40 IU/ml, IgA < 12 IU/ml No evidence of contact with the pathogen or of infection
IgG 40 - 100 IU/ml, IgA < 12 IU/ mlNo evidence of contact with the pathogen or of infection
IgG 40 - 100 IU/ml, IgA > 12 IU/ mlEvidence of contact with the pathogen or of infection
IgG > 100 IU/mlEvidence of contact with the pathogen or of infection

Neither a previous infection, nor vaccination provides lifelong protective immunity against whooping cough, although antibody titres often persist. It is therefore not possible to assess a patient’s immunity against pertussis using serology.

Test material

For the PCR:

  • Deep nasopharyngeal smear using a swab without a transport medium:
    Carefully insert the swab horizontally via the front sections of the nose to the back wall of the throat (posterior pharyngeal wall) and rotate. Withdraw the swab and insert it into the tube without any medium.
  • Nasal/throat rinsing fluid, nasal/throat aspirate

For serology:

  • 1 serum tube

Therapy
Antibiotic therapy with macrolides (e.g. clarithromycin or azithromycin) for up to 3 weeks after the start of coughing should be considered, as this will shorten the contagious period. The earlier the therapy begins during the illness, the sooner both the severity and the duration of the illness will be reduced. Oral penicillins and cephalosporins are not effective.

Prevention and vaccination
Chemoprophylaxis with macrolides is recommended for people who come in contact with the disease without protective vaccination. Particularly important is “nest protection” – vaccinating all people who come in contact with unvaccinated infants – since the disease is life-threatening and can be difficult to identify because of the apnoea attacks.
The acellular pertussis vaccine (TDaP/Tdap), which is available in Germany in combination with tetanus and diphtheria vaccines, is well tolerated. Basic immunisation should be established in early infancy, and boosters should be given at pre-school age and school age and once during the adult years. The recommendations of the Standing Committee on Vaccination (STIKO) at the Robert Koch Institute contain the exact vaccination intervals and the other indications.

Reporting obligation
In Berlin, Brandenburg, Mecklenburg-Western Pomerania, Saxony, Saxony-Anhalt and Thuringia, there is a duty to report all clinically diagnosed cases of pertussis, which applies to both doctors and laboratories, both when there is direct evidence of the pathogen (e.g. from the PCR) as well as when there is indirect evidence (from serology).


Literature
RKI Ratgeber für Ärzte (Guide for Doctors): Pertussis (Keuchhusten), updated: 03/09/2010, published by the Robert Koch Institute. www.rki.de
Empfehlungen der Ständigen Impfkommission (STIKO) am Robert Koch-Institut/ updated: July 2011
Guiso N., Berbers G., Fry, N.K., He, Q., Riffelmann, M., Wirsing von König, C.H.: What to do and what not to do in serological diagnosis of pertussis: recommendations from EU reference laboratories; Eur. J. Clin Mikrobiol Infect Dis 2011, 30: 307-312

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