Psittacosis differential diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S. [2]; Omodamola Aje B.Sc, M.D. [3]

Overview

Psittacosis must be differentiated from other diseases that cause atypical pneumonia and febrile illness without localizing signs and extrapulmonary manifestations such as gastroenteritis, hepatitis, meningitis, or encephalitis. The three main diseases to differentiate psittacosis from are Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella infection, as they tend to have similar clinical manifestations that can only be differentiated by taking appropriate histories and laboratory investigations. There are other conditions to watch out for which may also present similarly to psittacosis.

Differentiating Psittacosis from other Diseases

The following diseases must be differentiated from psittacosis based on the presentation of cough, fever, myalgia, and shortness of breath.

Disease	Clinical Manifestations							Lab findings			Imaging findings	Main treatment
	Cough	Sputum	Dyspnea	Sore throat	Headache	Confusion	Diarrhea	Hyponatremia	Leukopenia	Abnormal Liver function tests
Psittacosis	++	–	+	–	+++	+	Minimal	–	+	–	No changes seen	Doxycycline
C.pneumoniae pneumonia	+	+	+	+++	++	+	–	–	–	–	Minimal changes observed	Doxycycline, azithromycin
M. pneumoniae pneumonia	++	++	++	–	–	–	–	–	–	+	Bronchial wall thickening Centrilobular nodules Ground-glass attenuation Consolidation	Doxycycline
L. pneumophila infection	+	+++	+++	–	+	++	+	++	+	++	Often multifocal	Doxycycline
Influenza	++	++	++	++	++	±	±	–	–	–	Bi-basal air-space opacities Perihilar reticular and alveolar infiltrates	Zanamivir, oseltamivir
Endocarditis	++	++	+	–	–	–	–	–	±	±	Hazy opacities at lung bases bilaterally	Vancomycin
Coxiella burnetii infection	++	–	+	±	–	+/-	Minimal	–	±	±	Segmental or lobar opacification Occasional pleural effusions	Doxycycline
Leptospirosis	++	+	++	+	+	++	–	+++	–	–	Multiple ill-defined nodules in both lungs	Doxycycline, azithromycin, amoxicillin
Brucellosis	++	–	+	–	++	+	–	±	±	±	Soft miliary mottling Parenchymal nodules Consolidation Chronic diffuse changes Hilar or paratracheal lymphadenopathy Pneumothorax	Doxycycline, rifampin

Key;

+: Occurs in some cases

++: Occurs in many cases

+++: Occurs frequently