As regards the correlation between mortality and specific co-morbidities, there was a statistically significant positive correlation between mortality and old age (r = 0.633, smoking (r = 0.640), obesity (r = 0.712), diabetes mellitus (r = 0.685), renal failure (r = 0.705), chronic heart diseases (0.591), COPD (r = 0.523), malignancy (r = 0.692), kidney transplantation (r = 0.644) and liver cirrhosis (r = 0.525) (P < 0.05), (Table 3) .