A report by the the US Centers for Disease Control and Prevention (CDC) said that a rare virus has killed three people and sickened nearly 100 in Japan, the Philippines, the United States and the Netherlands over the past two years.
The culprit is human enterovirus 68 (HEV68), and its respiratory symptoms can be particularly dangerous to children, the CDC said in its Morbidity and Mortality Weekly Report.
In six separate clusters of the virus that showed up worldwide, patients commonly experienced cough, difficulty breathing and wheezing.
The highest number of cases were found in Japan, where local public health authorities reported more than 120 cases last year.
However, the CDC said it could only confirm clinical data for 11 of those patients, all children, one of whom died.
The Philippines had 21 cases in late 2008 and early 2009, causing two deaths, the CDC said.
Other cases surfaced in the Netherlands and the US states of Georgia, Pennsylvania and Arizona, for 95 total confirmed cases over two years.
The virus was first discovered in four children who were sick with pneumonia in California in 1962, but subsequent incidences have been rare and sporadic, according to the CDC.
"Identification of a large number of patients with HEV68 respiratory disease detected during a single season, such as described in this report, is a recent phenomenon," it added.
"Whether this increase in recognized cases is attributable to improved diagnostics or whether the clusters themselves represent an emergence of the pathogen is unknown."
The CDC said its report aimed to highlight HEV68 as "an increasingly recognized cause of respiratory illness" and urged clinicians to report cases of unexplained respiratory illness to public health authorities.
Human enterovirus is closely related to human rhinovirus, which causes the common cold.