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Quick Guide To Accurate Laboratory Diagnosis Of Whooping Cough

What is whooping Cough? 

Whooping cough, also known as pertussis, is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis. Accurate and timely laboratory diagnosis plays a crucial role in the management and control of this disease. This blog post aims to provide an overview understanding of laboratory diagnosis of whooping cough. We will also cover a brief on  the causative agent, epidemiology, as well as clinical presentation.

Laboratory diagnosis of Whooping Cough Pertussis
Whooping Cough: Highly contagious (Image: Urgent Omaha Care)

What causes whooping Cough?

Bordetella pertussis is a gram-negative bacterium responsible for causing whooping cough. It is transmitted through respiratory droplets from an infected person. B. pertussis attaches to the cilia lining the respiratory tract, leading to inflammation and the characteristic symptoms of the disease.

The who and where 

Whooping cough is a worldwide health concern, primarily affecting infants and young children. It can be severe and even life-threatening, especially in infants less than 1-year-old. Adolescents and adults can also contract the disease, and they may experience milder symptoms or even remain asymptomatic carriers, acting as potential sources of transmission to susceptible individuals. In Kenya, whooping cough is seen in non-immunized or under-immunized children and those with impaired immune systems. 

Clinical Presentation of Whooping Cough

The clinical presentation of whooping cough can vary depending on the age of the affected individual. Early symptoms may resemble those of a common cold, including runny nose, sneezing, and mild cough. As the disease progresses, the cough becomes more severe and may be followed by a high-pitched “whoop” sound during inhalation. Infants may also present with apnea (brief pauses in breathing) or cyanosis (blue tint to the skin) due to inadequate oxygen intake.


Diagnosis of Whooping Cough

The doctor takes into account the patients symptoms (see above), examination findings as well as imaging and laboratory tests. Pertusis vaccine is one of the KEPI panel, its important to establsih vaccination status as well

Laboratory testing for whooping cough

The process of testing proceeds through several steps as detailed below:-

1.Sample Collection:

To establish a laboratory diagnosis of whooping cough, appropriate samples need to be collected from the respiratory tract during the early stages of the illness. Nasopharyngeal swabs or aspirates are commonly used for this purpose. The samples should be collected using proper aseptic techniques and transported to the laboratory promptly to ensure accurate results.

Timing of specimen collection for culture

Ideally, specimens should be collected during the first 2 weeks of illness following cough onset. This is when viable bacteria are still present in the nasopharynx. After the first 2 weeks, sensitivity decreases and the risk of false-negatives increases.

If culture is planned, directly plate the collected NP swab or immediately place it into the transport medium. Laboratory scientists should plate NP swabs and aspirates within 24 hours of collection.

Culture has better specificity than PCR, but takes up to 7 days to obtain results.

Obtaining a nasopharyngeal specimen for isolation of Bordetella pertussis.
Obtaining a nasopharyngeal specimen for isolation of Bordetella pertussis. (Image: CDC)

2. Laboratory Analytical Methods:

Once the sample is delivered to the lab,  there are several laboratory methods are employed for the diagnosis of whooping cough. These include:

i) Serology: Serological tests measure the presence of specific antibodies produced in response to B. pertussis infection. Enzyme-linked immunosorbent assay (ELISA) and complement fixation tests are commonly used for this purpose. Serology can be particularly useful in diagnosing cases that present late or have a prolonged cough illness.

ii) Culture: Isolation of B. pertussis from clinical samples allows for definitive identification. It is the gold-standard in the identification of B. pertussis.  However, this method is time-consuming and requires specialized media and expertise.

iii) Polymerase Chain Reaction (PCR): PCR techniques enable rapid and sensitive detection of B. pertussis DNA in clinical samples. It offers high specificity and can detect the presence of the bacterium even during the early stages of infection. The downside is limited availability outside of major centers’ and research institutions. According to CDC, the PCR test also has lower sensitivity, increasing the chances of false negative results

Interpretation of Results:

Interpreting laboratory results for whooping cough diagnosis requires a comprehensive understanding of the various testing methods and their limitations. Positive culture or PCR results, along with compatible clinical symptoms, confirm the presence of B. pertussis infection. Serological tests can aid in the diagnosis of cases with prolonged cough illness, showing evidence of past infection or recent exposure.


Further Investigations:

In some cases, further investigations may be necessary to confirm the diagnosis or evaluate the extent of the disease. These may include:

  • Chest X-ray: Radiographic imaging can help assess lung involvement and detect complications such as pneumonia or pneumothorax.
  • Complete Blood Count (CBC): A CBC can reveal leukocytosis (elevated white blood cell count), which is often observed in whooping cough.
  • Pertussis Toxin (PT) PCR: This specialized PCR test can detect the presence of pertussis toxin gene variants in B. pertussis strains, providing valuable information for surveillance and strain characterization.

Where to get testing for whooping cough and the cost.

The basic serological test is widely available in most private and some public hospitals. In case of outbreaks, the national laboratory as well as KEMRI deploys mass testing in affected areas. PCR and culture for B. pertussis are not widely available in Kenya, the exception being research institutions or studies.

The cost of pertusis serological tests ranges from KES 500- 2000 depending on the facility and location.

It takes about 4-6 hours to get the serology and PCR results, culture takes atleast 7 days

A comprehensive list of laboratory pieces in Kenya is available here for more information

Recap of laboratory diagnosis of whooping cough

Laboratory diagnosis plays a vital role in identifying and managing whooping cough cases. Understanding the causative agent, epidemiology, clinical presentation, and appropriate sampling techniques is essential for accurate laboratory testing. 

Analytical methods such as culture, PCR, and serology aid in the diagnosis, while further investigations may be required to evaluate complications or confirm the diagnosis. By utilizing these laboratory diagnostic tools effectively, healthcare professionals can diagnose the disease and implement timely treatment. Laboratory surveillance is critical in keeping outbreaks of whooping cough under check.

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Disclaimer: The information provided on this medical blog is for general informational purposes only and should not be considered as a substitute for professional medical advice. Always consult with a qualified healthcare provider before making any healthcare decisions or taking any actions based on the information provided on this blog. The authors and publishers of this blog are not liable for any errors or omissions in the content or for any actions taken based on the information provided.