Melioidosis outbreak in Hong Kong: What is the cause?

On Nov. 17, the Hong Kong Department of Health’s Centre for Health Protection (CHP) provided another update regarding the investigation of the ongoing outbreak of melioidosis (Burkholderia pseudomallei), including a thirty-seventh patient as well as additional positive soil samples and negative water samples.  

One hypothesis for the cause of the outbreak is “climate change,” manifest as typhoons or storms causing respiratory infection from bacteria endemic in the soil. If accurate, then other places with Burkholderia pseudomallei in the soil that experience strong storms, such as parts of Thailand, Australia, India and the Americas, including the USA (Mississippi), are at risk for new and worse outbreaks of melioidosis. In fact, past outbreaks in Hong Kong and other places where the organism is endemic in the soil would have been expected after similar storms.

In a prior update, on Nov. 3, CHP reported:

“Melioidosis is an endemic disease in Hong Kong, and the bacteria could exist in soil in general. In the past five years (2017 – 2021), the number of cases recorded in Hong Kong ranged from three to 17 every year. The CHP reminded members of the public that according to literature, infection cases are more common after typhoons or storms. The bacterium Burkholderia pseudomallei of melioidosis in the soil and muddy water may become exposed to the ground after typhoons or storms, and the bacteria would spread easier with strong wind or storms. As such, the number of melioidosis cases may increase.”

With regard to genetic sequencing of seven environmental (soil) isolates and “some” patient isolates, the Nov. 17 update from CHP stated:

“With regard to the 32 soil samples, the team of the University of Hong Kong (HKU) yielded positive bacterial culture from seven samples. The whole genome sequencing conducted by the DH's PHLSB revealed that the bacteria of the environmental isolates and the human isolates of some patients are genetically highly similar.”

The traditionally excellent Hong Kong teams of infectious diseases scientists, clinicians and public health officials, as proven over the decades from influenza to SARS-CoV-1 in 2003 to SARS-CoV-2/COVID-19, means that this melioidosis investigation will continue until the exact cause for this specific outbreak is determined.  

Complete data on genetic sequencing from all the environmental and patient isolates of Burkholderia pseudomallei, and comparison with isolates from both inside and outside Hong Kong, will be epidemiologically helpful.