HMPV Pneumonia Associated with Older Age, Cigarette Use, Underlying Disease

Clinical features of human metapneumovirus (HMPV) infection have not been well documented for adults but results of a new study report that HMPV pneumonia infections were strongly associated with older age, current smoking, and underlying disease.

HMPV was first described in 2001 and is a common pathogen that causes acute respiratory tract infections in all age groups. Although infection is typically asymptomatic in the majority of patients, it can cause severe pneumonia in elderly and immunocompromised individuals.

To learn more about the clinical characteristics of HMPV infection, a team of investigators from South Korea conducted a cohort study in a hospital in South Korea. The team was focused on determining the characteristics of both clinical and radiologic features of HMPV pneumonia in immunocompromised and immunocompetent patients, which had not been explored in previous studies.

For the study period of January 2010 through February 2016 the investigators identified 850 adults infected with HMPV in a tertiary hospital, according to results published in the journal Emerging Infectious Diseases. The patients were classified into different groups based on respective underlying diseases which included immunocompetent patients, solid tumor patients, solid organ transplant recipients, and hematopoietic stem cell transplant recipients.

The investigators found that 696 of the 850 patients (82%) were diagnosed during the months of March and June, reinforcing a previous belief that infections followed seasonal patterns and were most commonly diagnosed during the spring months. Additionally, 89% of infections were found to be community-acquired and the remaining 11% of infections were nosocomial.

From the total population of HMPV-infected patients, 65% were hospitalized for a median of 7 days (range 4-13 days). The highest all-cause mortality rates were reported in hematopoietic stem cell transplant recipients with 30-day and 90-day mortality rates of 22% and 33%, respectively.

A total of 579 individuals (68.2%) were diagnosed with pneumonia, 72.5% of the population of immunocompetent patients and 63.1% of immunocompromised patients, respectively. An additional 203 individuals were found to have infections tied to other pathogens, according to the report.

When assessing characteristics of HMPV pneumonia, the investigators determined that oral ribavirin was used to treat 129 patients and intravenous immunoglobulin was used in 11 patients. Use of ribavirin was found to be more common in the 68 patients who required admission to the intensive care unit.

“In our study, use of ribavirin was more common in ICU-admitted patients, and mortality rates were also higher in patients who received ribavirin,” the authors write in the study synopsis. “However, this study was not designed to analyze the efficacy of ribavirin, and ribavirin might have been used more often for treatment in severely ill patients.”

The investigators also determined through univariate analysis that the median age of the patient was higher in those with pneumonia than in those with upper respiratory infections (66 vs 59 years, respectively).

It was also observed that HMPV pneumonia was significantly associated with current cigarette smoking and diabetes. The proportion of HMPV pneumonia cases was higher for immunocompetent patients than patients with solid tumors, as well.

CT imaging demonstrated that bilateral bronchial wall thickening, ground-glass opacities, and ill-defined centrilobular nodules were common in HMPV pneumonia. The authors indicate that the findings of bronchial wall thickening, bronchiolitis, and centrilobular nodules were likely caused by pathogenesis of HMPV pneumonia, affecting the airways and lung epithelia and inducing inflammatory cascades.

The investigators indicate that this study provided information on HMPV infection in both immunocompromised and immunocompetent individuals that were needed for early detection of HMPV infection and to determine pneumonia-related outcomes.