Microbiology
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Pathogens
A 17 year old boy presents to ED with a 4 week history of a persistent paroxysmal cough. You can hear the characteristic inspiratory whoop and suspect whooping cough. How would you confirm your diagnosis:
Answer:
Whooping cough is a notifiable disease. If there is any suspicion of infection because of clinical features, a notification form should be completed and sent to the local Public Health England (PHE) centre within 3 days. If the cough is of more than 2 weeks’ duration, anti-pertussis toxin immunoglobulin G (IgG) serology may be employed in people aged over 17 years. Anti-pertussis toxin IgG detection in oral fluid can be used in children aged 5 to 16 years.Bordetella Pertussis
Microbiology / Pathogens / Pertussis
Last Updated: 10th August 2019
| Microorganism | Bordetella Pertussis |
|---|---|
| Gram stain | Gram negative |
| Shape | Rod (coccobacilli) |
| Oxygen requirements | Obligate aerobe |
| Additional features | Fastidious organism, encapsulated, produces exotoxin |
| Reservoir | Nasopharynx |
| Transmission | Respiratory droplet route |
| Diseases | Whooping cough |
Transmission
Bordetella pertussis causes whooping cough, and is spread via the respiratory droplet route.
Pathogenesis
B. pertussis express fimbriae that aid their adhesion to the ciliated epithelium of the upper respiratory tract, and produce a number of exotoxins, causing the characteristic thickened bronchial secretions, paralysis of cilia and lymphocytosis.
Clinical Disease
The incubation period is about 7 - 10 days (range 5 - 21 days) and whooping cough is considered to be infectious for 3 weeks after the initial onset of symptoms. In the absence of an adequate vaccination programme, epidemics of whooping cough occur in children approx. every 3 - 4 years.
A 1 - 2 week cold-like prodromal illness (catarrhal phase) occurs before the paroxysmal phase which is characterised by repeated paroxysmal, prolonged severe coughing fits. Typically, paroxysms consist of a short expiratory burst followed by an inspiratory gasp, causing the 'whoop' sound. The paroxysms may be severe enough to cause cyanosis in children, and are frequently associated with post-tussive vomiting. This phase can last for up to 3 months, during which there is a gradual improvement in cough frequency and severity. Leucocytosis with marked lymphocytosis is common during this phase of the illness.
Complications include:
- Secondary bacterial bronchopneumonia
- Secondary bacterial otitis media
- Apnoea following coughing spasms
- Seizures
- Encephalopathy
- Unilateral hearing loss
- Complications due to violent prolonged coughing
- Pneumothorax, abdominal hernia formation, rectal prolapse, rib fracture, herniation of lumbar intervertebral discs, urinary incontinence, subconjunctival haemorrhage, facial/truncal petechiae, post-coughing vomiting leading to dehydration/malnutrition
Clinical Diagnosis
Whooping cough should be suspected if a person has an acute cough that has lasted for 14 days or more without another apparent cause, and has one or more of the following features:
- Paroxysmal cough.
- Inspiratory whoop.
- Post-tussive vomiting.
- Undiagnosed apnoeic attacks in young infants.
Clinical suspicion should be raised if the person is not fully immunized, or has been in contact with a person who is confirmed or suspected of having whooping cough.
Consider an alternative cause if symptoms are atypical, but be aware that very young children, adults, and people who have some immunity (due to prior infection or vaccination) may present with atypical symptoms (cough without whoop in infants and adults, apnoea in infants, or milder illness).
Laboratory Diagnosis
Whooping cough is a notifiable disease. If there is any suspicion of infection because of clinical features, a notification form should be completed and sent to the local Public Health England (PHE) centre within 3 days.
The local health protection team can advise on appropriate tests for confirmation and surveillance. This will depend on the person's age, the duration of symptoms, and on local laboratory facilities.
- If the cough is of 2 weeks’ duration or less, culture of a nasopharyngeal aspirate or nasopharyngeal/pernasal swabs is recommended for people of all ages. However, a negative result does not exclude pertussis.
- Real-time PCR testing of nasopharyngeal or throat swabs can also be used to confirm infection in people of all ages with symptoms of less than three weeks' duration.
- If the cough is of more than 2 weeks’ duration, anti-pertussis toxin immunoglobulin G (IgG) serology may be employed in people aged over 17 years. Anti-pertussis toxin IgG detection in oral fluid can be used in children aged 5 to 16 years.
- Be aware that serology and oral fluid test results may be confounded by receipt of a primary or booster dose of pertussis-containing vaccine within the last year. It is also more difficult to recover the organism in vaccinated compared with unvaccinated children, which may affect culture results.
Thus, whooping cough is confirmed when a person with clinical features of pertussis has:
- Bordetella pertussis isolated from a nasopharyngeal aspirate or nasopharyngeal/pernasal swab,or
- Detection by real-time PCR of the pertussis toxin S1 promoter region (ptxA-pr), and the insertion element IS481, or
- Anti-pertussis toxin IgG detected in serum or oral fluid in the absence of vaccination within the past year.
Management
Arrange admission if the person:
- Is 6 months of age or younger and acutely unwell.
- Has significant breathing difficulties (for example apnoea episodes, severe paroxysms, or cyanosis).
- Has a significant complication (for example seizures or pneumonia).
- Note: inform the hospital of the need for appropriate isolation before the person is admitted.
If admission is not needed, prescribe an antibiotic if the onset of cough is within the previous 21 days.
- A macrolide antibiotic is recommended first-line:
- Prescribe clarithromycin for infants less than 1 month of age.
- Prescribe azithromycin or clarithromycin for children aged 1 month or older, and non-pregnant adults.
- Prescribe erythromycin for pregnant women.
Offer information and advice to the person and their family/carers:
- Advise rest, adequate fluid intake, and the use of paracetamol or ibuprofen for symptomatic relief.
- Inform the person that, even with antibiotic treatment, whooping cough is likely to cause a protracted non-infectious cough that may take several weeks to completely resolve. Symptoms are likely to be less severe and resolve more quickly if the person has been immunized or has had pertussis before.
- Advise the person to seek medical advice if they develop clinical features of any complications.
- Advise that children and healthcare workers who have suspected or confirmed whooping cough should stay off nursery, school, or work until 48 hours of appropriate antibiotic treatment has been completed, or 21 days after onset of symptoms if not treated.
- People who work in other settings should avoid contact with infants under one year of age who are unvaccinated or partially vaccinated until 48 hours of appropriate antibiotic treatment has been completed, or 21 days after onset of symptoms if not treated.
Prevention
The routine childhood vaccination schedule for pertussis is shown below:
| Time frame | Vaccine |
|---|---|
| 2 months | DTaP/IPV/Hib |
| 3 months | DTaP/IPV/Hib |
| 4 months | DTaP/IPV/Hib |
| Preschool | DTaP/IPV |
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
