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106 Chapter 3: Respiratory system

Management Pathophysiology
1 Hospitalisation is required for severely ill patients or Influenza viruses develop new antigenic variants at reg-
where compliance is a particular problem. ular intervals through random mutations and antigenic
2 Standard regimen is with 2 months of rifampicin, iso- drift. Human immunity depends largely on the haemag-
niazid, ethambutol and pyrazinamide, and a further glutinin (H) antigen and the neuraminidase (N) antigen
4months of rifampicin and isoniazid alone. These are on the viral surface. Major shifts in these antigenic re-
taken 30 minutes before breakfast to aid absorption. gions in influenza viruses occur through acquisition of
3 Multi-resistant strains require sensitivity assessment anew H or N from animals such as birds, horses and
and should be treated with three drugs to which the pigs.Thesecancauseapandemic,whereasantigenicdrift
organism is sensitive for a full 6 months to avoid de- causes the milder annual epidemics. Influenza B only oc-
velopment of further resistance. curs in humans and only undergoes antigenic drift.

Prevention
Clinical features
In the United Kingdom, vaccination with BCG (Bacille
Rapid onset of fever usually >38 C, cough, headache,
◦
Calmette–Gu´ erin) has been given to Heaf negative
shivering and myalgia start after an incubation period of
12 year olds since 1954. It is also offered to infants up
1–3 days. Other upper and lower respiratory symptoms
to6weeks after birth (without prior skin testing) in ar-
may develop. Individuals are infective for 1 day prior to
eas with a high incidence of tuberculosis. Contact trac-
and for around 1 week after symptoms commence.
ing of cases is essential for screening of all close family
members and individuals who share kitchen and bath-
Complications
room facilities by history, chest X-ray and tuberculin
Otitis, sinusitis and viral pneumonia are common. In-
test.
fluenza may exacerbate underlying respiratory disease
Patients with chest X-ray evidence of previous TB who
including asthma and chronic obstructive pulmonary
become immunosuppressed, e.g. renal dialysis, steroid
disease.
treatment or organ transplant, may have daily isoniazid
Secondary bacterial infection particularly with Strep.
treatment to prevent reactivation of latent infection.
pneumoniae and H. influenzae is common follow-
ing influenza pneumonia. Less commonly, secondary
Prognosis
Staph. aureus infection which has a mortality rate of
Five per cent of patients do not respond to therapy, only
20%.
1% due to resistance, the remainder due to failed com-
pliance. Post-viral syndrome: Debility and depression may de-
velop after the acute illness, and take weeks to months
to resolve.
Influenza Post-infectious encephalomyelitis is rare but does
occur.
Definition
Acute infection caused by the influenza viruses type A
or B (RNA orthomyxovirus). Investigation
Diagnosis is confirmed by detection of virus in nasal
or throat swabs by culture, antigen detection or PCR.
Aetiology
Influenza A causes worldwide annual epidemics and is Retrospective diagnosis can be made by a rise in spe-
infamous for the much rarer pandemics, the most seri- cificcomplement-fixingantibodyorhaemagglutininan-
ous of which occurred in 1918 when ∼40 million people tibody measured 2 weeks apart, but this is usually un-
died worldwide. Influenza B is also associated with an- necessary.
nual outbreaks that are usually milder in nature than
those caused by influenza A. Influenza C is of doubt- Management
ful pathogenicity in humans. Spread is by respiratory Bed rest, antipyretics such as paracetamol for symp-
droplets. toms. Fluids may be needed.