Investigations in infectious respiratory diseases : Part 1 Flashcards
What is tuberculosis?
TB is a disease that is caused by mycobacterium tuberculosis
It affects the lungs mostly but can affect any organ
What is mycobacterium tuberculosis and why can it not be detected using normal gram staining?
Mycobacterium tuberculosis is a small rod shaped bacteria that has a waxy coating, making it resistant to the acid used in acid staining - therefore it is called acid fast bacilli due to this mechanism being called “acid fastness”
How do you test for microscopy of TB and how does this work?
Ziehl-Neelsen method
- can be performed on sputum, CSF, urine, gastric washings in children
- Turns TB bright red against a blue background
What are the limitations of using the Ziehl-Neelsen method?
Cannot distinguish between Acid-Fast Bacillus that are dead or viable, therefore you cannot use it in the treatment progress part of monitoring TB
How would a patient present if they had a form of TB?
Gradual, worsening onset
General: fever, lethargy, anorexia, weight loss, enlarged and tender lymph nodes
Pulmonary: cough (usually chronic), sputum (initially dry, then purulent or blood-stained), breathlessness, pleuritic chest pain
Extra-pulmonary: genitourinary (urinary symptoms), musculoskeletal (joint pain), neurological (headache, reduced GCS, focal neurology), cardiac (chest pain), gastrointestinal (abdominal pain, bloating), rash
What are the different types of risk factors for contracting TB?
PMHx
- Immunosuppression (HIV)
- Chronic conditions (diabetes)
DHx:
- Immunosuppressive drugs (steroids)
SHx:
- TB contact
- Time in high incidence area (South Asia)
- current/history of homelessness
- imprisonment
- Drug/alcohol misuse
- Travel history
- Occupation
What is the difference between:
- Primary/active TB
- Latent TB
- Secondary TB
- Miliary TB
Primary/Active TB:
- Active infection within different areas of the body
- Able to be cleared by the immune system
Latent TB:
- Immune system has been able to stop the progression of the disease
- Patient becomes asymptomatic
Secondary TB:
- TB is reactivated from latent form
Miliary TB:
- Infection has spread (disseminated) and the immune system is unable to control it
- Severe form
How it TB spread?
Through droplets - coughing/sneezing
What is the first line investigation for suspected active TB and what would this show?
1) Chest x-ray
Primary TB may show patchy consolidation, pleural effusions and hilar lymphadenopathy
Reactivated TB may show patchy or nodular consolidation with cavitation (gas filled spaces in the lungs) typically in the upper zones
Disseminated Miliary TB give a picture of “millet seeds” uniformly distributed throughout the lung fields
What other investigation would you choose to do alongside a CXR if a patient presented with suspected pulmonary TB?
Sputum samples
- three samples for TB microscopy and culture (AAFB) at 8 to 24 hour intervals
What immunological test can be done to help the diagnosis of TB and how does it work?
Mantoux skin test:
- Tuberculin is injected into the skin (component of TB)
- Result read 48-72 hours post injection to allow for an immune reaction
Positive = large area of induration
Does not tell you whether the TB is active or latent
What is IGRA and when would you use it in the diagnosis of TB?
IGRA - Interferon-gamma release assay (TB Quantiferon ELISA)
- Used to diagnose latent TB in patients 18-65 who have moved to the UK from a high risk country
If a patient is IGRA positive, what is the next step?
LFTS
HIV
CXR
What are the two treatment options for latent TB?
3 months rifampicin/isoniazid combination therapy
6 months isoniazid monotherapy
What is the management of acute pulmonary tuberculosis?
R - Rifampicin (6 months)
I - Isoniazid (6 months)
P - Pyrazinamide (2 months)
E - Ethambutol (2 months)
What are the side effects of taking Rifampicin? (3 marks)
- Hepatitis
- Red/orange discolouration of the skin, teeth, salvia…
- Reduces the effects of other drugs by inducing cytochrome p450 –> consider this with contraceptive pill
“Red-an-orange-pissin”
What are the side effects of taking Isoniazid? (2 marks)
- Hepatitis
- Peripheral neuropathy –> “I’m-so-numb-azid”
What needs to be given alongside Isoniazid to prevent a certain complication and why?
Pyridoxine (vitamin B6)
- Prescribed as a prophylactic to help prevent peripheral neuropathy
What is a side effect of Pyrazinamide? (2 marks)
- Hepatitis
- Gout
What is a side effect of Ethambutol?
- Visual disturbance (reduced visual acuity and colour blindness)
“eye-thambutol”
What is Malaria and what is it caused by?
Infectious disease caused mostly by Plasmodium falciparum (P.falciparum)
What is the transmission process of Malaria?
1) Female Anopheles injects infected sporozoites into host
2) Sporozoites travel to the liver of host
3) Either lie dormant as hypnozoites if injected by P.vivax & P.ovale
4) Mature in the liver to merozoites that enter the host’s blood and infect RBC, reproduce over 48 hours
5) RBC rupture and spread more merozoites causing haemolytic anaemia
(why patients have fever spikes every 48 hours)
What is the incubation period for P.falciparum?
12-14 days
How would a patient present with suspected malaria? (4 marks)
- Fever/sweats
- Headache
- Vomiting
- Malaise
What clinical features would be seen in a patient with suspected Malaria?
- Anaemia (Pallor)
- Hepatosplenomegaly
- Mild jaundice (due to release of bilirubin
What are the features of major/severe malaria in adults? (3 marks)
- Impaired consciousness
- Hypoglycaemia
- Renal impairment
Who is more at risk at contracting severe Malaria?
- Pregnant women
- Children
- Immunocompromised
What is the gold standard investigation to detect Malaria?
Microscopy of thick and thin Giemsa-stained blood film
What is the difference between the thick and thin blood films?
Thick - identifies the burden of the disease (how many RBC are infected)
Thin - identifies the species of mosquito
How many samples of the blood films are sent and when?
If the first are negative, further testing should be arranged 12-24 hours later and again a further 24 hours to rule out infection
3 samples sent over 3 consecutive days
What bottles are used to collect the malaria blood films?
EDTA
Aside blood films, what is another investigation used to detect malaria and how does it work?
Rapid diagnostic test (RDT)
- detects parasite antigens
- 15-20 minutes
What is the non-medical and medical management for Malaria?
Non-medical
- Discuss with infectious disease specialist
- Inform Public Health England
Medical (IV in complicated malaria
- Artesundate
- Quinine dihydrochloride
What non-medical and medical treatment is used as prophylaxis for Malaria?
Non-medical
- Mosquito spray
- Pre-travel advice
- Mosquito nets and barriers
Medical (anti-malarials)
- Malarone
- Mefloquine
- Doxycycline
What is Cystic Fibrosis?
CF is an autosomal recessive inherited disorder that is caused by a mutation in the CF chloride transporter protein.
What is the consequence of the mechanism that causes cystic fibrosis? (3 marks)
Thick pancreatic and biliary secretion –> lack of digestive enzymes
Thick airway secretions –> bacterial colonisation –> more LRTI
Congential bilateral absence of the vas deferens in males –> male infertility
How is cystic fibrosis diagnosed at birth and what is the first sign of cystic fibrosis?
New-born screening
- Meconium ileus
- Meconium (stool) not passed within 24 hours and is thick and sticky causing an obstruction
- abdominal distention and bloating
What are the symptoms of cystic fibrosis? (5 marks)
- Chronic cough
- Recurrent RTI
- Loose, greasy stools
- Abdominal pain and bloating
- Failure to thrive
What are the signs of cystic fibrosis?
- Low weight/height
- finger clubbing
- abdominal distention
- crackles/wheeze on auscultation
What is the gold standard test for diagnosing cystic fibrosis and how does it work?
Sweat test
- Pilocarpine applied to arm/leg skin patch
- Small current passed through to generate sweat
- Sweat is tested in the lab for chloride concentration
Positive for CF if chloride concentration is more than 60mmol/L
What are the two major microbial colonisers in patients with cystic fibrosis that cause infections?
- Staph aureus
- pseudomonas aeruginosa
What is whooping cough and what is it caused by?
Respiratory infection caused by Bordatella Pertussis
How is whooping cough transmitted?
Respiratory droplet
What is the presentation of whooping cough in the three different stages?
1) Mild cough and coryzal symptoms for 1-2 weeks
2) Paroxysmal stage 2-8 weeks - sudden and recurring attacks of coughing with little/no inspiratory effort causing the “whooping” noise
- can cause vomiting
3) Cough starts to subside after weeks/months
When would you suspect whooping cough in a child? (4 marks)
- Cough not improving
- Watery rhinorrhoea
- whoop apnoea
- post-tussive vomiting
If a patient who is less than 4 months has had a cough for less than 3 weeks, how would you test them for whooping cough? (2 marks)
- PCR
- Culture of nasopharyngeal aspirate
If a patient who is more than 4 months presents with a cough of less than 3 weeks, how would you test for whooping cough? (3 marks)
- PCR
- Culture of nasopharyngeal aspirate
- serology if more than one year since last vaccination
If a patient who is less than 4 months presents with a cough lasting more than 3 weeks, how would you test for whooping cough? (2 marks)
- PCR
- Culture of nasopharyngeal specimen
If a patient who is more than 4 months presents with a cough lasting more than 3 weeks, how would you test for whooping cough and what would you look for?
- Serology if more than 1 year since last vaccination –> B.pertussis igG
What is Alpha-1 antitrypsin deficiency?
Alpha-1 antitrypsin deficiency is an inherited disorder (autosomal recessive) which affects the lungs, liver, and occasionally skin
What is the role of alpha-1-antitrypsin?
Protease inhibitor that prevents the secretion of elastase from neutrophils that digests connective tissues
Made in the liver and offers protection from the elastase digestion
How does Alpha-1 antitrypsin deficiency affect the liver?
Mutant protein is instead made that can get trapped in the liver leading to liver cirrhosis and hepatocellular carcinoma
How does Alpha-1 antitrypsin deficiency affect the lungs?
Protease enzymes have the ability to damage connective tissue in the lungs leading to bronchiectasis and emphysema
What condition is A1AT deficiency more commonly associated with?
COPD
In what following situations would you consider A1AT deficiency? (4 marks)
Emphysema in:
- <45 years
- non smoker
- family hx of emphysema or liver disease
- unexplained chronic liver disease
What are the three main ways you can test to diagnose A1AT deficiency?
1) serum-alpha 1-antitrypsin <18mmol/L
2) Lung function tests (spirometry)
3) Imaging - CT thorax
When would you do a viral respiratory PCR? (3 marks)
- COVID
- RSV
- Influenza
What is a viral respiratory PCR?
Fast, useful diagnostic test used for patients presenting with upper respiratory tract symptoms
