Infectious disease Flashcards
What is tuberculosis?
-Chronic granulomatous disease
What causes tuberculosis?
-Aerobic mycobacterium tuberculosis complex
What are the 3 different mycobacterium tuberculosis complex bacteria called?
- M. Bovis
- M. tuberculosis
- M. africanum
How is tuberculosis caught?
- Spread by infected droplets coughed up by infected patients when the granulomas rupture
- Can live on environmental surfaces for long periods of time
How might a primary infection of tuberculosis present?
- Asymptomatically
- Mild flu-like illness
What is the pathogenesis of TB?
-Droplets inhaled into the alveoli of the lungs
-Macrophages engulf organisms and attempt to control them in the hilar lymph nodes
-Granulomas form
>Some bacteria are eliminated, some lay dormant, some disseminate
Why do only a small proportion of patients progress to active TB?
-The body is usually good enough to control the mycobarcterium but when someone is immunosuppressed (AIDS, long term steroids, age), the TB escapes the granulomas and spreads to the apices.
Why does active TB spread to the apices of the lungs?
-TB is aerobic and the apices receive more oxygenation
What are risk factors for TB?
- Close contact of TB patient
- Ethnic minority groups
- Homeless patients, alcoholics, drug abusers
- HIV
- Extremities of age
- Comorbid patients especially immunosuppressed
What are the systemic clinical features of TB?
-Long progressive history of:
>Fever
>Night sweats
>Weight loss
What are the pulmonary presentations of TB?
- Haemoptysis
- 3/52 productive cough
- Breathlessness
- Chest pain
How does Miliary TB present?
- Kidneys (most common extra-pulmonary site): sterile pyuria
- Meningitis
- Pott disease in lumbar vertebrae
- Addisons
- Hepatitis
- Lymphadenitis
- Arthritis
- Erythema Nodosum
What are the TB differentials?
- Cancer
- Atypical pneumonias
- Fibrotic lung disease
What should be the first thing that is done if you suspect TB in a patient?
- Allocate them a side room
- Barrier nurse with advanced masks
What investigations should be done for a patient suspected with TB?
- Chest Xray
- Ziehl-Neelsen Stain for acid fast bacilli
- Culture on Lowenstein-Jensen slope
- Rapid diagnostic nucleic acid amplification test (expensive)
How long does culture results take for TB?
- 4-6 weeks.
- If have a high suspicion and a positive Ziehl-Neelsen stain and CXR treat for TB
What colour does Ziehl-Neelsen stain turn if Tb is present?
- TB mycobacterium are aerobic acid fast bacilli and will turn red on staining.
- Other acid fast bacilli will also turn red on staining
Apart from sputum samples, what other samples should be cultured if TB is suspected?
- Lymph node biopsies
- Aspirated pus
- Early morning urine
When is the montoux test useful?
-For contact tracing. Identifies anybody with a previous exposure to the mycobacterium
What is the management for TB?
- Side room and TB
- Notify PHE
- RIPE drug treatment
What tests should be done before commencing on TB treatment?
- LFTs
- U&Es
What are the RIPE drugs?
- Rifampicin
- Isoniazid
- Pyrazinamide
- Ethambutol
How long should the RIPE drugs be taken for and why?
- 2 months: Pyrazinamide and ethambutol
- 6 months: Rifampicin and isoniazid
- Drugs only target active TB. Longer treatment time increases chance of latent TB becoming active and destroyed
Which RIPE drugs are bactericidal and which are bacteriostatic?
-Bactericidal >Rifampicin >Isoniazid >Pyrazinamide -Bacteriostatic >Ethambutol
What are the side effects of rifampicin?
-Red body secretions
-Induction of liver enzymes affecting:
>Oestrogens, steroids, phenytoin, anticoagulants
-Hepatitis
What are the side effects of isoniazid?
- Hepatitis
- Neuropathy
What drug reduces the risk of isoniazid induced neuropathy?
-Pyridoxine
What are the side effects of pyrazinamide?
- Hepatitis
- Arthralgia
- Gout
- Rash
What are the side effects of ethambutol?
-Optic neuritis
>Usually resolves if drug is stopped immediately.
What patient group is multi drug resistance likely to occur?
-HIV patients
When is treatment failure likely to happen?
- Incorrect prescribing
- Lack of compliance
How is latent TB managed in a patient without HIV?
-6/12 isoniazid OR 3/12 rifampicin + isoniazid
How is latent TB managed in a patient with HIV?
-6/12 isoniazid
What treatment should be given to patients with known contact to a TB patient?
-6/12 rifampicin
What is HIV
Human Immunodeficiency virus
How does HIV infection lead to AIDs?
-Causes the immune system to fail and not fend off infections
What is the most common HIV strain in the world?
-HIV 1
How is HIV transmitted?
-Sexual intercourse >MSM (most common) >Heterosexual intercourse (M->F usually) -IVDU -Pregnancy >placenta, delivery, breast milk -Blood transfusions
What are the 9 steps of HIV replication?
- Attachment
- Entry
- Uncoating
- Reverse transcription
- Genome integration
- Transcription of RNA
- Splicing of mRNA and translation
- Assembly of new viruses
- Budding
What is HIV formed of?
- An outer envelope
- An inner core containing RNA and RNA reverse transcriptase
What is the HIV surface glycoprotein that binds to CD4 receptors?
-GP120
What immune cells contain CD4 receptors?
- T cells
- Lymphocytes
- Dendritic cells
- Monocytes
- Macrophages
What bacteria is someone that has
a HIV infection presdisposed to?
- Penumoniae
- H. Influenzae
What is the category A section of HIV natural history?
-Primary infection or seroconversion
>Non-specific symptoms: malaise, fever, maculopapular rash, myalgia, headache, meningitis
What is the clinical latency phase?
- Mainly asymptomatic
- Lasts from 6weeks to 10 years
What happens in the category B phase?
- Rise in viral load, fall in CD4 count.
- Development of clinical features due to immunosuppression
What are some examples of category B diseases?
- Bacillary angiomatosis
- Candidiasis
- Oral hairy leukoplakia
- Herpes zoster (>1 dermatome)
- ITP
- Listeriosis
- PID
- Peripheral neuropathy
What are examples of category C diseases?
- Candidiasis of bronchi, trachea, lungs, oesophagus
- Invasive cervical carcinoma
- CMV
- Encephalopathy
- HSV
- Histoplasmosis
- Kaposi’s sarcoma
- Burkitt’s lymphoma
- TB
- PJP
- Recurrent pneumonia
- Recurrent salmonella septicaemia
- Toxoplasmosis of the brain
What are some of the clinical features of AIDS?
- Aseptic meningitis
- Retinal cotton wool spots
- Aphthous ulcerations
- Neutropenia
- HIV enteropathy
- Renal impairment
- Reduced adrenal function
- Myocarditis, cardiomyopathy
- Infections
- Coinfections ie Hep B
How is HIV diagnosed?
-Antibody assays
(detectable 6-12 weeks post infection)
-Viral genotype analysis
How is HIV monitored?
- CD4 count 3 monthly
- <200=greatest risk of HIV related pathology
- rapidly falling CD4 of <350 needs antiretroviral therapy
- HIV RNA 3-6 montly
What is a normal CD4 count?
-500
How is HIV managed?
- Drugs
- Social and psychological care
- Contacting tracing and sexual education
- Prevention of infections
What are the different types of HIV drugs?
- Nucleoside reverse transcriptase inhibitors
- Non-Nucleoside reverse transcriptase inhibitors
- Protease inhibitors
- Fusion inhibitors
- Integrase inhibitors
What is the ideal treatment combination for HIV?
-2NRTI and 1 NNRTI/protease inhibitors
What is the HIV treatment goal?
-Suppress viral load to <50 copies/ml
How do nucleoside reverse transcriptase inhibitors work?
-Inhibits synthesis of DNA by reverse transcriptase and acts as DNA chain terminators
How do non-nucleoside reverse transcriptase inhibitors?
-Bind directly to and inhibit reverse transcriptase
How do protease inhibitors work?
-Acts as competitively on HIV enzyme which prevents production of functional viral proteins and enzymes
What are some examples of nucleoside reverse transcriptase inhibitors?
- Abacavir
- Didanosine
What are some examples of non-nucleoside reverse transcriptase inhibitors?
- Efavirenz
- Etravirine
What are some examples of protease inhibitors?
- Atazanavir
- Darunavir
When should post exposure prophylaxis be taken?
- Combination of oral antiretrovirals immediately for up to 4 weeks
- Testing at 12 weeks
Where are sterile sites within the body?
- Ureter
- CSF
- Peritoneal fluid
- Pericardial fluid
- Pleural fluid
- Synovial fluid
- Bone marrow
- Blood
What are gram +ve bacteria?
- Streptococci
- Staphylococci
How are gram +ve bacteria differentiated?
- Staph = catalast +ve
- Strep = catalase -ve
What conditions can Staph. aureus cause?
- IE
- Wound infections
- Abscesses
- Osteomyelitis
- TSS
- Pneumonia
- Scalded skin syndrome
- Food poisoning (3 hour incubation period
What condition does staph. saprophyticus cause?
-UTI