Discussion
Our Study is the first to evaluate the Charlson Comorbidity Index in adult patients hospitalized with acute respiratory infection secondary to HMPV and look at its predictive value on mortality in this patient population. CCI was initially proposed in 1987 and was tested for its ability to predict risk of death from comorbid disease in a 10-year follow-up Cohort (9). It has been validated in patients with renal cell carcinoma (10) post radical cystectomy (11) and internal medicine related complications post hip arthroplasty (12). It proved to be good at prediction of long-term functional outcome for the stroke population (13). It is also proved to independently predicts short- and long-term mortality in acutely ill hospitalized elderly adults (14).
While the CCI was not found to be associated with an increased risk of mortality in our cohort of HMPV infection, an elevated CCI was shown recently to predict poor prognosis in hospitalized patient with coronavirus disease (COVID19) and end stage renal disease on hemodialysis (15) and in general in patients with COVID 19 in a recent meta-analysis (16). In another study by Setter et al, although the Charlson Comorbidity Index Score was different between survivors and non survivors in patients with severe acute respiratory infections, its performance was not optimal (17). In that study most patients studied had influenza pneumonia and few had HPMV. The low number of patients in our study precludes us to make strong conclusions regarding the value of CCI, however it was noted that most patients had a high CCI with a mean of 4.6 which explains the high mortality rate of 22% which is not unusual and was even reported to be 50% in an outbreak among elderly patients in a long-term care facility (LTCF) (18).
This mortality rate even exceeds that related to COVID19 in LTCF which was reported recently to be 14% (153751/1090729) (19). It is worth noting that unlike COVID19, HMPV causes severe disease in young children ranging from croup like, asthma exacerbations, bronchiolitis and pneumonia with a peak age of ranging from 5 to 22 months old which is older than those with RSV (20). Unlike infections due to SARS-Cov2, HMPV infections are seasonal with winter epidemics occurring from December to April in the northern hemisphere at the same time or just after RSV epidemics. This is likely due to the lower transmissibility of HMPV which is usually transmitted by contact with contaminated surfaces as opposed to SARS-Cov2 which is more transmissible, mainly via respiratory droplets and contact (21) and possibly airborne (22). In Our Study we noted that patients requiring ICU care and mechanical ventilation and those with bacterial or fungal superinfection had worse outcome and were more likely to die which is not unusual and seen in patients with influenza and COVID19 as well (23). In addition, having higher fever and abnormal CXR may indicate a worse outcome. The CXR findings were similar to what is seen with influenza or RSV lower respiratory tract infections which is different than radiographic findings described with COVID19 which are easily recognized due to its characteristic peripheral distribution (24). Other features that distinguish HMPV infection from the COVID19 due to the Omicron variants specifically is that most patients complained of cough and dyspnea, 85.7% and 71% respectively while rhinorrhea with nasal congestion, sore throat and myalgia were even less frequently reported in 38%, 14.2% and 23.8% respectively which is usually more prominent with the Omicron variants of SARS-Cov2 related infections with 70% of patients presenting with sore throat (25).