My father had recurring caugh the blood tests held negative for any decease. He was subjected to antibiotics for 3 weeks and the said caugh would again recurr after a week. This continued for a very long period about 6 months. Although antibiotics were given the caugh did not subside. But latter we assumed that, caugh was due to alergy and applying allergy medicines with caugh syrup did a marvelllous job to sibside caugh.