Respiratory and GI Tract Infections

1
Respiratory and GI Tract Infections

• Mark Pallen

2
The Common Cold

• Causative Organisms
• Rhinoviruses
• Coronaviruses
• viruses also responsible for more severe
  illnesses
• adenoviruses, coxsackieviruses, echoviruses,
  influenza parainfluenza viruses, RSV,
  enteroviruses
• Many cases unknown cause

• Clinical features
• rhinorrhoea, sore throat, sneezing, cough
• management
• Self-limiting
• Avoid aspirin in children (risk of Reyes
  syndrome)
• Avoid antibiotics

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Sore Throat

• Clinical features pharyngitis tonsillitis
• Causative organisms
• mostly viral
• bacterial causes
• Streptococcus pyogenes
• (a.k.a. Group A beta-haemolytic streptococci)
• Less commonly Corynebacterium diphtheriae, Group
  C and G beta-haemolytic streptococci,
  Arcanobacterium haemolyticum, Fusobacterium
  necrophorum

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Streptococcal pharyngitis

• Diagnosis Throat swab
• Plate out on Blood agar
• Beta-haemolysis (complete haemolysis)
• Lancefield grouping of capsular antigen
• Rapid diagnostic tests with fluorescent antibody
  or latex agglutination

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Streptococcal pharyngitis

• Management
• Oral Penicillin V for 10 days (to prevent
  Rheumatic Fever)
• Can cause serious wound infections, so...
• Isolate patients in hospital
• Health workers should stay off work, and MUST
  STAY OUT of the operating theatre!

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Streptococcal pharyngitis

• Complications
• Paratonsillar abscess (quinsy)
• Scarlet Fever
• fine, red, raised rash on trunk extremities,
  feels like coarse sandpaper
• Sequelae
• Rheumatic Fever or Glomerulonephritis
• diagnosis anti-streptolysin O (ASO) antibody
  titres

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Diphtheria

• Acute toxin-mediated disease caused by
  Corynebacterium diphtheriae
• Gram-positive aerobic bacillus
• Incubation period 2-5 days
• Typically involves pharynx and tonsils
• leathery adherent membrane, which can cause
  respiratory obstruction
• Toxin effects
• Myocarditis
• Neuropathy

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DiphtheriaManagement

• Diphtheria is a medical emergency!
• Urgent need for antiserum tracheostomy
• Seek expert advice immediately you suspect it!
• Do NOT WAIT for bacteriological confirmation
• Antibiotic treatment
• Erythromycin
• Diphtheria is a public health emergency!
• Contact Public Health authorities immediately you
  suspect it!
• Notifiable disease
• Need for contact tracing, prophylaxis
• Prevention routine childhood vaccination (
  adult boosters?)

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Glandular Fever

• a.k.a. infectious mononucleosis
• Caused by Epstein-Bar virus
• Spread by kissing
• (incubtaion period 1 month)
• Clinical features
• Fever, malaise, sore throat, cervical
  lymphadenopathy
• Rarely, splenomegaly, splenic rupture, haemolytic
  uraemia
• Ampicillin and amoxycillin rash
• Diagnosis Serology
• Traditionally, detection of heterophil antibodies
  (agglutinate sheep erythrocytes) Paul Bunnell or
  monospot tests
• More specific anti-EBV antibodies can now be
  detected

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Otitis Media Sinusitis

• Local spread of organisms from URT , e.g.
• Streptococcus pneumoniae
• Haemophilus influenzae
• viruses probably commonly involved
• Clinical features
• Fever, local pain, dizziness, deafness
• Treatment
• Short course of co-amoxiclav
• Surgery, e.g. insert grommets

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Acute Epiglottitis

• Infective emergency
• Caused by Haemophilus influenzae capsular type B
  (Hib)
• Now very rare due to Hib vaccine program
• Can lead to acute respiratory obstruction
• Patients must be intubated ( tracheostomy)
• DO NOT attempt to take throat swabs
• DO NOT attempt to have a look/see

• Diagnosis
• take blood cultures
• H. influenzae requires rich medium
• (e.g. lysed blood or chocolate agar)
• Requires X and V growth factors on nutrient agar
• Management
• Intravenous cefotaxime or ceftriaxone
• Isolate the patient
• Prevention
• Hib vaccine

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Croup Bronchiolitis

• RSV flu/paraflu viruses
• Clinical Features
• cold-like symptoms progress to harsh barking
  cough, worse at night, or when agitated
• wheeze in bronchiolitis
• can progress to respiratory obstruction or
  exhaustion, requiring hospitalisation
• Diagnosis
• Immunofluoresence or PCR on nasopharyngeal
  aspirate

• Management
• Supportive, e.g. intubation, oxygen, assisted
  ventilation
• in severe or high-risk cases, nebulised
  ribavirin (for RSV)
• Epidemiology
• Annual epidemics of RSV in winter months

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Pertussiswhooping cough

• Caused by Bordetella pertussis
• a fastidious Gram-negative rod
• Clinical Features
• Catarrhal stage for 2 weeks
• Paroxysmal stage for 2-6 weeks or longer
• Convalescent stage
• Sequelae
• weight loss, surgical emphysema, brain damage

• Diagnosis
• Lymphocytosis
• Culture of B. pertussis from pernasal swab
• Management
• erythromycin in catarrhal stage
• TOO LATE in paroxysmal stage!
• BUT still prevents infectivity
• Supportive treatment for paroxysms
• Prevention
• Vaccination as part of DTP x3

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Acute LRTI

• Various clinical syndromes
• Bronchopneumonia
• Diffuse patchy consolidation
• S. pneumoniae, H. influenzae
• Lobar pneumonia
• Typically S. pneumoniae
• Interstitial pneumonia
• Characteristically viral
• Lung abscess
• Atypical pneumonia

N.B. tuberculosis, pneumonia in the
immunocompromised and hospital-acquired pneumonia
will be covered later in the course
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Pneumococcal pneumonia

• Diagnosis
• Blood cultures sputum
• Strept. pneumoniae
• a.k. a. the pneumococcus
• Seen on Gram stain
• Grows on blood agar
• Draughtmans colonies
• Bile soluble
• Optochin-sensitive

• Treatment
• Traditionally benzylpenicillin
• Risk of resistance means blind therapy with
  cefotaxime or ceftriaxone
• Prevention
• Polyvalent pneumococcal vaccine
• Offered to those at risk
• Elderly (gt65)
• splenectomised patients
• Diabetics, alcoholics, CSF leak, COAD

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Atypical Pneumonia

• Caused by
• Mycoplasma pneumoniae (unusual bacterium)
• Legionella pneumophila (fastidious GNR)
• Chlamydia psittaci, C. pneumoniae
• Empirical treatment of all community-acquired
  pneumonia should include erythromycin to cover
  atypicals
• Diagnosis
• antigen detection culture for L. pneumophila
• Serology PCR for all atypicals

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Influenza

• Epidemiology
• Yearly epidemics in winter months
• antigenic drift point-mutational changes
• Intermittent worldwide pandemics with increased
  morbidity and mortality
• antigenic shift recombination in birds, pigs
• totally new antigen types
• Rates of infection highest among children
• Severity increased greatly among elderly, those
  with medical conditions

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Influenza

• Two types (A and B) and many subtypes
• Type and subtype related to surface antigens
  (hemagglutinin and neuraminidase)
• Immunity decreases likelihood and severity of
  disease
• Immunity to one type or subtype offers little to
  no immunity to others

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Influenza

• Clinical features
• Abrupt onset fever, myalgias, headache, malaise,
  sore throat, rhinitis, nonproductive cough
• Complications
• viral pneumonia and/or bacterial superinfection
• typically S. pneumoniae
• Hospitalisation and Death
• greatest among elderly

• Antiviral agents
• shorten or prevent disease
• traditional
• amantadine (A)
• neuraminidase inhibitors
• oseltamivir (A and B) and zanamivir (A and B)
• Influenza vaccination
• gt 65 years old
• Others at risk of complications
• Health care staff?

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Tuberculosisnatural history clinical features

• Caused by Mycobacterium tuberculosis
• Primary infection
• asymptomatic or non-specific symptoms fever,
  malaise, weight loss, night sweats
• Inhalation of tubercle bacilli
• leads to lung infection
• Ingestion of tubercle bacilli
• tonsils cervical nodes
• small bowel with mesenteric nodes
• Direct implantation into skin

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Progressive Primary Infection

• local erosion by primary focus
• pleural cavity pleurisy
• pericardium pericarditis
• bronchus tuberculous bronchopneumonia (highly
  infectious)

• disseminated infection
• miliary tuberculosis
• multiple discrete granulomas resembling millet
  seeds
• metastatic infection
• tuberculous meningitis
• bone joint
• kidney
• uterus/testis

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Post-Primary Infection

• as a result of reactivation of latent infection
• latent period between primary infection and
  reactivation can be several decades
• certain factors predispose to reactivation
• immunosuppression, e.g. AIDS, cytotoxics
• malnutrition
• alcoholism
• diabetes
• old age

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Diagnosis

• Clinical features
• Constitutional
• Fever, Malaise, Weight loss, Night sweats
• Focal
• Cough, Haemoptysis, Chest pain
• Radiological features
• Patchy opacities mainly in the upper zone
• cavitation, calcification, hilar shadowing
• diffuse nodular shadowing in miliary TB

• Extra-pulmonary Tuberculosis
• Greater emphasis on histology
• Caseating granulomas are diagnostic

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Lab Diagnosis Specimens

• large multiple specimens in sterile containers
• pulmonary TB
• early morning sputum specimens (x3)
• gastric washings
• bronchoscopy specimens
• a single negative sample does not rule out
  tuberculosis

• extra-pulmonary TB
• EMUs, LNs, BM, CSF
• unfixed!
• special risk to lab staff
• Category 3 pathogens
• In sealed leak-proof container
• Danger of Infection label
• In plastic bag

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Diagnosis Microscopy

• stain poorly with the Gram-stain
• Acid-fast bacilli (AFBs) rely on Acid-fast
  staining
• Ziehl-Neelsen stain

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Diagnosis Culture

• Lowenstein-jensen slopes
• M. tuberculosis grows after 4-6 weeks, rough buff
  an tough, breadcrumb-like colonies
• Kirschners broth

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Tuberculin Testing

• Mantoux test, Heaf test
• Purified protein derivative (PPD)
• delayed type (Type IV) hypersensitivity
• Positive
• Induration not erythema
• past or present infection
• or previous BCG vaccination
• Negative
• no previous infection or vaccination

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TuberculosisTreatment

• Multi-drug regimens used
• prevent the emergence of resistance during
  therapy more effective
• Initial Phase 3 drugs for 2 months
• Continuation Phase 2 drugs for 4-7 months

• Seek expert advice from chest physician!
• compliance problems drug toxicity common
• repeated consultations
• risk of resistance

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Prevention of tuberculosis

• Eradicate poverty
• Control TB in cattle
• Early diagnosis treatment of cases
• Side-room isolation of open smear-positive
  cases in hospital
• Selective screening with CXR

• Follow up of contacts of cases
• TUBERCULOSIS IS A NOTIFIABLE DISEASE
• Notification of the Public Health authorities is
  a legal requirement!!
• Immunisation with BCG
• traditionally at 11-13 years
• at birth in at risk infants

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Two new interlocking problems

• Effect of HIV pandemic on TB
• Greatest public health disaster since the bubonic
  plague...
• Evil synergy between TB and HIV infection
• Reactivation rates much higher in HIV-positives
• 10 lifetime risk of reactivation in
  HIV-negatives
• 8 annual risk in HIV-positives
• TB more aggressive in HIV-positives

• Emergence of multi-resistant TB
• In many areas, eg NYC, Nepal, Florida,
  multi-resistant strains have emerged, resistant
  to most, if not all, anti-TB drugs
• several outbreaks of multi-resistant TB in the
  USA, often centred on HIV-positive patients
• Medical prison staff have caught fatal
  untreatable tuberculosis!