Comparison of morbidity and mortality of rhinovirus infection to 2009 pandemic H1N1 influenza A at an academic tertiary referral center

Background: Viruses other than influenza A can present as an influenza-like illness (ILI) (fever >37.8C and cough/sore throat).  Molecular testing has made feasible the diagnosis of common respiratory viruses.  This is important in tertiary referral centers that treat immunocompromised patients. 

Objective: To compare the morbidity and mortality of rhinovirus infection to influenza A among patients served in a tertiary referral center.

Methods: Retrospective chart review of patients with a positive respiratory viral test result by xTAG® RVP (Luminex Corp, Austin, TX) from 9/9/09 until 10/9/09.  The Mantel-Haenszel chi-square test (categoric variables) and the Wilcoxon rank sum test (continuous variables) were used for comparisons.   

Results: Six-hundred and thirty specimens were received for respiratory viral testing.  There were 128 (20%) positive tests for influenza A, 81 (13%) for rhinovirus, and 11 (1.7%) other viruses.  There were 201 (91%) adults and 19 (9%) children (<18y).  The mean age for the influenza group was lower compared to the rhinovirus group (Table 1).  Gender and race were similar in the 2 groups.  More antiviral treatment was given to the influenza group (p<0.001) but there was no difference in the receipt of antibacterial agents.  More fever and ILI criteria were met in the influenza group than the rhinovirus group (p<0.001).  While there was no difference in underlying comorbidities between the groups, more individuals were immunocompromised (transplant, HIV, actively treated malignancy) in the rhinovirus group (p<0.001).  There were more bacterial or fungal co-infections in the rhinovirus group as compared to the influenza group (p=0.01).  Hospital admission rates between the groups were not significantly different, nor were admissions to the ICU.  Mortality rates were similar in both groups. 

Conclusions: Patients with 2009 pandemic H1N1 influenza A and rhinovirus had similar hospitalization rates and admissions to the ICU.  There were more immunocompromised patients and bacterial co-infections in the rhinovirus group, which could account for the similarity of the clinical course to influenza.  Rhinovirus infection, while usually mild, in a tertiary referral center demonstrates morbidity and mortality similar to influenza A.    

Table 1.

Characteristic	Influenza group number (%)	Rhinovirus group number (%)	P value
Number	128	81	--
Age	34.2 y ± 16.8 y	41.2 y ± 15.4 y	P=0.003
Fever	97 (76%)	32 (42%)	P<0.001
ILI criteria met	76 (59%)	14 (18%)	P<0.001
Antiviral therapy	58 (45%)	11 (14%)	P<0.001
Antibacterials	33 (26%)	23 (30%)	NS
Immunocompromised	10 (7.8%)	17 (22%)	P=0.003
Coinfection	11 (8.6%)	17 (21%)	P=0.01
Hospital admission	38 (30%)	24 (31%)	NS
ICU stay	7 (5.5%)	7 (9.1%)	NS
Death	2 (1.6%)	2 (2.6%)	NS

NS=not significant