Clinical use
Investigation for infection with Bordatella pertussis.
Background
Pertussis, commonly known as whooping cough (“violent cough”) has been associated with high morbidity and mortality, particularly in infants. Whooping cough is a highly contagious disease that is caused by the fastidious Gram negative coccobacilli Bordetella pertussis and more rarely Bordetella parapertussis that colonise the respiratory tract. The main symptoms include malaise, fever followed by long bursts of coughing and choking leaving the infected person gasping for breath with a characteristic whoop sound.
B. pertussis usually infects and causes severe respiratory disease in young children, with infants under six months of age at most risk of severe complications. The infection can occur in adolescents and adults who exhibit milder symptoms of flu-like illness followed by a prolonged cough. The incubation period of pertussis is on average between 7–10 days (range 5–21 days).
In addition to sampling for pertussis, it is recommended that consideration is given to testing the patient for respiratory viruses and Mycoplasma pneumoniae according to local procedures. A pertussis-like syndrome can be associated with respiratory syncytial virus (RSV), adenovirus, parainfluenza virus, and rhinovirus/enterovirus infections. In addition, the bacterium M. pneumoniae is known to cause similar symptoms. It is to be noted that co-infection with B. pertussis and RSV is more likely to be associated with particularly severe disease.
The testing strategy utilised for pertussis investigations generally depends on the duration of cough.
- If the cough has been present for 0-2 weeks – bacterial culture can be performed. After the first 2 weeks the sensitivity of bacterial culture decreases and the risk of false-negatives increases.
- If the cough has been present for 0-4 weeks – PCR testing can be undertaken, PCR is more sensitive than culture, but is less likely to be positive in patients with symptom duration of more than 4 weeks.
- If the cough has been present for 2-12 weeks – serology to detect anti-pertussis IgG (anti-PT IgG) can be considered
- Please note Interpretation of anti-PT IgG levels among infants and younger children may be confounded by the presence of maternal antibodies or recent primary and booster vaccination, or show an atypical response.
Early laboratory diagnosis is important for control and prevention of whooping cough.
Patient preparation
A pernasal swab is inserted through a nostril and advanced along the floor of the nose until it reaches the nasopharynx. It has been suggested that the swab is held against the posterior nasopharynx for up to 30s or until the patient coughs. In practice, it is more likely that a patient will only be able to tolerate this for a few seconds.
Nasopharyngeal specimens
Nasopharyngeal exudate may be obtained using a suction catheter inserted through the nose. The exudate is collected in a sterile plastic trap in which the specimen is transported to the laboratory, or in a sterile clear plastic universal container.
Specimen requirements
A pernasal swab, nasopharyngeal aspirate, nasopharyngeal swab and/or blood, as appropriate for the test performed.
For bacterial culture any one of the following:
- Pernasal/nasopharyngeal (blue topped) Copan e-Swab
- Nasopharyngeal aspirate in a sterile universal container
For PCR any one of the following:
- Pernasal/nasopharyngeal (blue topped) Copan e-Swab
- Nasopharyngeal aspirate in a sterile universal container
For serology:
- Gold top serum separator blood
If processing is delayed, refrigeration of samples for bacterial culture is preferable to storage at ambient temperature.
A pernasal swab is inserted through a nostril and advanced along the floor of the nose until it reaches the nasopharynx.
The specimen collector should avoid exposure to direct coughs from the patient.
Minimum volume
For aspirates: minimum volume of 1 ml.
For blood: minimum 400 µL of serum
Limitations and restrictions
If processing is delayed, refrigeration is preferable to storage at ambient temperature.
Turnaround time
- Bacterial culture: 7 days
- PCR: 2 days
- Serology: 10 days
Analysing laboratory
Bacterial culture
Microbiology Lab, James Cook University Hospital, Marton Road, TS4 3BW
PCR
Micropathology Ltd, Venture Centre, University of Warwick Science Park, Sir William Lyons Road, Coventry, CV4 7EZ
Serology
RVPBRU: Respiratory and Vaccine Preventable Bacterial Reference Unit, 60 Colindale Avenue, London, NW9 5HT
Additional information
Please see the bacteriology e-swab user guide.
For a more detailed description of the investigation of whooping cough please see government guidance SMI B 6: investigation of whooping cough.