ANSWER 25
This man has Legionella pneumophilapneumonia. Community-acquired pneumonia is
most commonly caused by Streptococcus pneumoniaeorHaemophilus influenzae, but atyp-
ical pneumonias account for about 5–15 per cent of cases. The 4-day prodromal illness is
typical of Legionellapneumonia (2–10 days) compared to pneumococcal pneumonia which
tends to present abruptly with fever and shortness of breath. Legionella infection presents
with malaise, myalgia, headache and fever. Patients may develop diarrhoea and abdominal
pain. As the illness progresses the patient develops a dry cough, chest pain, shortness of breath
and acute confusion. Other potential complications include nephritis, endocarditis and
myocarditis. On examination, the patient is usually dehydrated, tachycardic and tachypnoeic
with widespread rhonchi and crackles. The diffuse infiltrates on chest X-ray suggest atypical
pneumonia, whereas a lobar pattern tends to occur with streptococcal pneumonia. Hypo-
natraemia occurs in cases of severe pneumonia and is a poor prognostic factor. Hypocalcaemia
is another distinctive biochemical abnormality in this condition. Confusion and raised urea
are markers of severity. The high CRP is consistent with a severe infection, and the lym-
phopenia is a clue to the fact that this patient has an atypical pneumonia. The patient’s arte-
rial blood gases showed marked hypoxia. This patient presumably acquired his infection
while on holiday in Spain. Legionellaoutbreaks have often been due to infected water tanks
in warm climates in institutions such as hotels and hospitals.
This man is acutely unwell and needs to be admitted to a high-dependency unit. He needs
to receive high concentration of inspired oxygen, and also intravenous fluids to correct his
dehydration. He may require mechanical ventilation. He should be started on intravenous
antibiotics. These should cover the common community-acquired pneumonias until the pre-
cise microbiological diagnosis is obtained and the antibiotics can then be rationalized. A
standard combination is cefuroxime and clarithromycin. Blood cultures should be sent, and
blood sent to screen for antibodies to atypical organisms such as Legionella,Mycoplasma,
Chlamydia psittaciand influenza. Ten to fourteen days later a further blood sample should
be sent and a fourfold rise in antibody titre is evidence of current infection. A faster diag-
nosis is made by testing broncheoalveolar lavage fluid, blood and urine for the presence of
Legionellaantigen.
- Legionellais one of the atypical causes of pneumonia.
- It should be suspected if there is an outbreak in an institution, or if a case of pneumonia
fails to respond to antibiotics. - Legionellapneumonia has a 2–10-day prodromal illness.
- Lymphopenia, evidence of nephritis, and a diffuse pattern of infiltrates on chest X-ray are
other clues to the diagnosis.