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Complications associated with influenza infection
Q1: What do the chest radiograph (fig 1b) and computed tomogram of the thorax (fig 1c; see p 100) show and how would the clinical and radiological findings be best treated?
The chest radiograph on admission (fig 1A) showed right middle lobe consolidation. The second chest radiograph taken six days later (fig 1B) shows that bilateral cavitating masses have developed. These were confirmed by computed tomography to be multiple lung abscesses (fig 1C), the largest of which was 10 × 8 cm in the left lower lobe.
Lung abscesses are areas of suppuration and necrosis with subsequent cavity formation. An air-fluid level is seen radiologically. They can occur in previously normal lung. They are often found after aspiration pneumonia or bronchial obstruction, due to either a foreign body or malignant lesion, but can occur in cases of primary pulmonary infection with Klebsiella pneumoniae or Nocardia asteroides, in cases of septicaemia with Streptococcus milleri, or as staphylococcal metastases in cases of Staphylococcus aureus septicaemia.
It is unusual for S pneumoniae pulmonary infection to cause a primary lung abscess. More commonly it causes an empyema, which is pus within the pleural cavity requiring drainage.
Lung abscesses should be initially treated conservatively with antibiotics and intensive chest physiotherapy to facilitate drainage.1 As more than 90% of lung abscesses will be caused at least in part by anaerobic bacteria, antibiotic treatment should include metronidazole, as well as aerobic organism cover, such as a penicillin or cephalosporin.
Antibiotics should be given to all patients, whatever the causative organism. This treatment should be initially intravenous, until the temperature settles and the patient clinically begins to improve. This will usually take about four to eight days. Antibiotics are then given orally for a further six to eight weeks, until the chest radiograph has cleared completely, or abnormalities become small and stable.2
Lung abscesses should not be treated surgically initially, unless there are complications with massive haemoptysis, empyema, or bronchopulmonary fistula. Ten per cent of patients are found to be unresponsive to medical therapy and may require surgical drainage of the abscess.
Failure of medical treatment is associated with large cavities of greater than 6 cm, abscesses associated with an obstructing lesion, recurrent aspiration pneumonia, development of an empyema, or prolonged symptom complex before presentation.
Lung abscesses are associated with a 15% to 20% mortality rate. The prognosis of patients with lung abscesses often depends on their underlying condition. Debilitated or immunocompromised patients have a worse prognosis, as do those with larger abscesses, in a right lower lobe location, infected by P aeruginosa, S aureus, or K pneumoniae.3
Primary lung abscesses often become colonised by P aeruginosa. This is found in the oropharynx of debilitated patients, where it is a commensal organism, often along with Proteus species and K pneumoniae. They require combination antibiotics along with treatment of the underlying condition.
This man's chest radiograph returned to normal after one month with medical treatment alone.
Q2: Is the high influenza A titre relevant to this case?
It is well documented that influenza A infection can predispose an individual to subsequent respiratory tract infection, which often results in pneumonia.4 This may be caused by the influenza virus itself or by secondary infection due to Streptococcus pneumoniae, S aureus, or Haemophilus influenzae. All can cause considerable mortality and morbidity, even in the young and previously healthy.
Q3: What is the cause of his acute renal failure?
He had acute tubular necrosis causing his acute renal failure. This was due to the haemodynamic disturbance caused by septicaemia. This man became dialysis independent almost one month after his original presentation.
Q4: What is the cause of his abnormal liver function tests?
In cases of S pneumoniae pulmonary infections, there may be associated jaundice around day 4 to 5. The exact cause of this is unknown, but it is often associated with right lower lobe consolidation. It is unusual for bilirubin to rise above 100 μmol/l and the other liver function tests are usually normal.5
Influenza with secondary S pneumoniae pneumonia and acute renal failure.