Table 3.
Differential diagnosis of severe influenza/influenza like illnesses
| Clinical Features | Influenza (Human Seasonal/Swine) | Avian Influenza (H5N1) | SARS | HPS |
|---|---|---|---|---|
| Epidemiology | 2 d | <7 d | 5 d | 4 d |
| Incubation period (mean) | (1–4 d) | (2–5 d) | (2–10 d) | (2–15 d) |
| Recent exposure | ||||
| Influenza | + | − | + | − |
| Birds | − | + | + | − |
| Rodents | − | − | − | + |
| Asian travel | − | + | + | − |
| Symptoms | ||||
| Biphasic illness | − | + | ± | − |
| Fever/chills | + | + | + | + |
| Profound weakness | + | − | − | + |
| Headache/muscle aches | + | + | + | + |
| Dry cough | + | + | − | + |
| Sore throat | + | + | − | − |
| Runny nose | + | ± | − | − |
| Hemoptysis | ± | ± | − | − |
| SOB → early | + | + | − | − |
| → late | ± | ± | + | + |
| Substernal discomfort/burning | ± | − | − | ± |
| Pleuritic chest pain | ± | − | − | + |
| Loose stools/diarrhea | ± | + | ± | + |
| Abdominal pain | − | − | − | + |
| Signs | ||||
| Fever >39°C/102°F | + | + | ± | ± |
| Conjunctival suffusion | + | + | + | − |
| Injected oropharynx | + | + | − | +a |
| Laboratory testsf | ||||
| Leukopenia | ±∗ | + | − | +d |
| Relative lymphopenia | + | + | + | − |
| Atypical lymphocytes | − | − | − | − |
| Immunoblasts | − | − | − | + |
| Thrombocytopenia | ± | ± | ± | + |
| Mildly elevated serum transaminases (AST/ALT) | ± | + | + | + |
| Elevated LDH | − | + | + | + |
| Elevated CPK | + | + | + | + |
| CXR | ||||
| Minimal/no infiltrates (early) | + | + | + | + |
| Bilateral patchy infiltrates (late) | + | + | + | +e |
| Focal segmental/lobar infiltrates | −b | −b | +c | − |
Abbreviations: CPK, creatinine phosphokinase; CXR, Chest radiograph; HPS, hantavirus pulmonary syndrome; LDH, lactate dehydrogenase; SARS, severe acute respiratory syndrome; SOB, shortness of breath.
*Usually normal WBC count.
Data from Cunha BA. Pneumonia essentials. 3rd edition. Sudbury (MA): Jones & Bartlett; 2010.
a
With exudates.
b
Unless bacterial CAP.
c
Infiltrates often ovoid or round.
d
Leukocytosis later with hemoconcentration and increase in severity.
e
Noncardiogenic pulmonary edema.
f
HI test for influenza A negative in avian influenza (H5N1); use PCR to diagnose avian influenza (H5N1).