Several observational studies demonstrated that Oseltamivir had a beneficial effect during 2009-A/H1N1 pandemics, but there are still controversies with seasonal subtypes (A/H3N2 and B).
The aim of this observational retrospective study was to detect clinical and antiviral-response differences among the current circulating viral subtypes during two consecutive seasons (2015/16-2016/17). Seventy-five hospitalized patients were recruited in a tertiary hospital: 25 influenza A/H1N1-2009, 25 A/H3N2 and 25 influenza B. All patients received oseltamivir.
Children with influenza-B infection were older than those with A/H1N1 and A/H3N2 (168 months (p25-27: 59-196) vs 39 (18-64) and 27 (16-85), respectively; p<0.01). 45/75 had preexisting conditions, mainly neurological. Rates of pre-existing conditions did not differ between subtypes.
The leading cause of hospitalization was respiratory insufficiency (39/75), with similar proportion between the groups. Digestive manifestations were frequent (24/75), but diarrhea was only described in A/H1N1 (5/25;p=0.03). Neurological symptoms tended to be more frequent in patients with influenza A (11/50 A vs 1/25 B;p=0.06). Acute myositis only occurred with influenza B infection (5/25;p<0.01).
Bacterial co-infection (mainly pneumococcal) was more frequent in patients with influenza A (11/50 vs 1/25;p=0.06).
9/75 patients required intensive-care. No differences between subtypes were found. Nevetheless, none of the 5/9 previously healthy patients had influenza B. No mortality was found.
There was a correlation between the delay in starting oseltamivir treatment and the duration of the disease for all subtypes (rho-Spearman A/H1N1:0.58, p<0,01; A/H3N2:0.51, p=0,01; B:0.49, p=0,04).
Extra-pulmonary symptoms and severity of influenza disease may vary depending on the subtype, especially in previously-healthy patients. Delays in starting oseltamivir treatment increased length of symptoms, regardless of the subtype.