Acute respiratory infection caused by the human metapneumovirus: Analysis of 39 cases.

Dear Editor,

The human metapneumovirus (hMPV) was first described in 2001 in respiratory secretions, although previous serological studies showed that it was already circulating in humans since 1950.1, 2 The hMPV is responsible for acute respiratory infections (ARI) and presents a worldwide seasonal distribution, predominating in the winter. It mainly affects children under 5 years of age, making it the second viral cause after the RSV.1, 2

ARI caused by hMPV in adults is a rare entity with a 3–10% incidence. This value is similar to that described for RSV (5%) and lower than influenza viruses (2%) during the winter season.1, 2 Although most ARI caused by hMPV in adults are asymptomatic or with few clinical manifestations, they may have high morbidity and mortality (about 10%) in nursing homes and among the elderly in general.1, 2

We report a prospective study on ARI caused by hMPV in adults (>15 years of age) during the period between January 2014 and March 2016. A throat swab was taken from each patient who came to the emergency room with suspected ARI to detect the presence of respiratory viruses. The diagnostic technique used was a commercial PCR-type genomic amplification in real time (Allplex™ Respiratory Panel; Seegene, Seoul, South Korea). Medical records and epidemiological data of patients with hMPV in their respiratory sample were reviewed.

The study analyzed 2125 patients. Of these, 1020 (48%) were considered positive for respiratory viruses. hMPV was detected in 39 cases (3.8% of those positive and 1.8% of all patients). These 39 cases accounted for 21% of all hMPV detected in this study (79% in paediatric population).

Regarding sex distribution, 22 (56.4%) were women; the average age was 61.7 years (range 20–86 years). Coinfection with other respiratory viruses (4 rhinovirus and 2 adenovirus) was detected in 6 cases (15.4%). 89.7% of cases were detected between the months of February and April. Of the patients studied, 21 (53.8%) required hospitalization, and of these, 4 (19%) were admitted to the intensive care unit. No patient died as a consequence of or during the respiratory infection associated with hMPV. The main clinical symptoms and diseases are shown in Table 1 . 31 patients received antibiotic treatment (79.5%): clavulanic acid (48%) and levofloxacin (45%). 5 patients were considered immunosuppressed (12.8%) and only one of them had no predisposing factors.

Table 1

Main symptoms and diseases detected in the 39 patients infected with human metapneumovirus.

Symptoms
Fever > 38 °C	23 (58.9)
Dyspnoea	14 (35.8)
Cough	13 (33.3)
Expectoration	8 (20.5)
Cold/flu symptoms	8 (20.5)
Shortness of breath	3 (7.6)
Diarrhoea	2 (5.1)
Headache	2 (5.1)
Disorientation	2 (5.1)
Diseases
Pneumonia	14 (35.8)
Bronchitis	9 (23.1)
Cold/flu symptoms	8 (20.5)
Tracheobronchitis	6 (15.3)
Pharyngotonsillitis	1 (2.5)
Shortness of breath	1 (2.5)

Data are expressed as number of cases (%).

The percentage of hMPV detection in our study was 3.8%, similar to that already reported in larger studies.1, 2 Compared to other viruses causing ARI in the adult population of our geographic area, we can observe an incidence of 7.8% for RSV, 7% for coronavirus and 0.38% for bocavirus.

Among the respiratory diseases, hMPV has been described to cause pneumonia, bronchitis, tracheobronchitis and respiratory distress conditions.1, 2 Pneumonia (35.8%) represented the main disease associated with hMPV in our study, followed by bronchitis and tracheobronchitis (23.1 and 15.3%, respectively). The frequency of hospitalization ranges from 20% to 55%, depending on the age and condition of the patient1, 2; in our group, it was 53.8%, and 19% of them were in the intensive care unit. This percentage is much higher than in the ARI caused by RSV (6.5%), Coronavirus (8%) or bocavirus (0%).

ARI caused by hMPV appear to affect mainly the adult population with some underlying disease.1, 2 Asthma, COPD and chronic heart diseases were present in 51.2% of our patients, besides the ailments typical to their age, including hypertension (43.5%) or diabetes mellitus (30.7%). 5 patients were considered immunocompromised (12.8%), all affected by leukaemia or lymphoma and one colon cancer.

Since there is no specific antiviral against hMPV, the only treatment is prevention of possible bacterial superinfection.1, 2 79.1% of our patients received antibiotic treatment with amoxicillin/clavulanic acid and levofloxacin. The mild to moderate nature of respiratory infections caused by hMPV in our study could determine the absence of deaths associated with this virus.

Conflict of interests

The authors declare no conflict of interest in connection with the results obtained in this study.