Multiple regression factor analysis indicated that the use of hormones (OR 4.001, 95% CI: 1.505–10.632), neutropenia or agranulocytosis (OR 7.472, 95% CI: 2.710–20.602), hemoglobin (Hb) < 90 g/L (OR 3.270, 95% CI: 1.256~8.516), and C-reactive protein (CRP) >15 mg/L (OR 3.253, 95% CI: 1.209~8.751) were independent risk factors that were associated with severe pneumonia. The gene discussed is GSTM1; the disease is Absence of circulating granulocytes.