Comparative evaluation of acute respiratory distress syndrome in patients with and without H1N1 infection at a tertiary care referral center

H1N1 subtype of influenza A virus has clinical presentation ranging from mild flu like illness to severe lung injury and acute respiratory distress syndrome (ARDS). The aim of our study was to compare the demographic characteristics, clinical presentation, and mortality of critically ill patients with (H1N1+) and without H1N1 infection (H1N1-). We retrospectively analyzed medical charts of patients admitted in "Swine Flu ICU" with ARDS from August 2009 to May 2010. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay was used for detection of H1N1 virus in the respiratory specimens. Clinical data from 106 (H1N1, 45; H1N1+, 61) patients was collected and compared. Mean delay in presentation to our hospital was 5.7 ± 3.1 days and co-morbidities were present in two-fifth of the total admissions. Sequential Organ Failure Assessment (SOFA) score of patients with and without H1N1 infection was comparable; 7.8 ± 3.5 and 6.6 ± 3.1 on day 1 and 7.2 ± 4.5 and 6.5 ± 3.1 on day 3, respectively. H1N1+ patients were relatively younger in age (34.2 ± 12.9 years vs. 42.8 ± 18.1, P = 0.005) but presented with significantly lower PaO(2):FiO(2) ratio (87.3 ± 48.7 vs. 114 ± 51.7) in comparison to those who subsequently tested as H1N1. The total leucocyte counts were significantly lower in H1N1+ patients during the first four days of illness but incidence of renal failure (P = 0.02) was higher in H1N1+ patients. The mortality in both the groups was high (H1N1+, 77%; H1N1, 68%) but comparable. There was a mean delay of 5.7 ± 3.1 days in initiation of antivirals. Patients with H1N1 infection were relatively younger in age and with a significantly higher incidence of refractory hypoxia and acute renal failure. Mortality from ARDS reported in our study in both the groups was high but comparable.