Baseline characteristics
All the included studies provided information about the gender of
patients. The pooled results revealed that the proportion of male in
patients was 0.58 (95% CI 0.55, 0.60) (I2=69%,
p<0.01) (Fig.2) (Table 2). Moreover, all the included studies
also provided information about chronic respiratory diseases,
hypertension, and endocrine system disease. The pooled results revealed
that the proportion of patients with chronic respiratory diseases,
hypertension, and endocrine system disease was 0.01 (95% CI 0.01, 0.02)
(I2=0%, p=0.91), 0.14 (95% CI 0.07, 0.24)
(I2=94%, p<0.01), and 0.09 (95% CI 0.07,
0.10) (I2=45%, p=0.02), respectively. Of the eligible
trials, eight provided information about cardiovascular disease,
malignant tumour, and digestive system disease. The pooled results
revealed that the proportion of patients with cardiovascular disease was
0.08 (95% CI 0.03, 0.17) (I2=95%, p<0.01),
malignant tumour was 0.02 (95% CI 0.01, 0.04)
(I2=52%, p=0.03), and digestive system disease was
0.05 (95% CI 0.03, 0.09) (I2=79%, p<0.01).
(Fig.3A,B,C,D,E, and F) (Table 2).
Of the eligible trials, 2 studies provided a detailed age profile of
patients with severe pneumonia. Data from one of the studies revealed
that 28.8% developed severe pneumonia in patients over the age of 65,
and only 13.9 % developed severe pneumonia in patients under the age of
65[10]. Another study suggested that 69.0% developed severe
pneumonia in patients over the age of 70, and only 34.2 % developed
severe pneumonia in patients under the age of 70[13]. Thus, the
above hinted that older patients are more likely to develop severe
pneumonia. But the data cannot be pooled due to the lack of further
detailed information. Further subgroup analysis revealed that the
proportion of severe patients with chronic respiratory system disease
was 0.04 (95% CI 0.02, 0.08) (I2=0.00%, p=0.28),
cardiovascular disease was 0.08 (95% CI 0.04, 0.15)
(I2=43%, p=0.06), malignant tumour was 0.03 (95% CI
0.01,0.06) (I2=0.00%, p=0.17), digestive system
disease was 0.03 (95% CI 0.00, 0.19) (I2=76%,
p<0.01), endocrine system disease was 0.16 (95% CI 0.11,0.21)
(I2=0.00%,p=0.66), and hypertension was 0.29 (95% CI
0.20,0.39) (I2=52%,p=0.04). The proportion of
non-severe patients with chronic respiratory system disease was 0.01
(95% CI 0.00, 0.04) (I2=63%, p=0.01), cardiovascular
disease was 0.02 (95% CI 0.01, 0.03) (I2=0.00%,
p=0.27), malignant tumour was 0.01 (95% CI 0.00,0.04)
(I2=55%, p=0.02), digestive system disease was 0.05
(95% CI 0.02, 0.13) (I2=87%, p <0.01),
endocrine system disease was 0.06 (95% CI 0.05,0.08)
(I2=0.00%,p=0.06), and hypertension was 0.17 (95% CI
0.11,0.25) (I2=70%,p <0.01) (Table 3).