Hong Kong has recorded a fourth locally acquired case of chikungunya fever and expert epidemiologists suggest it may stem from a new infection source rather than the previous cluster of three cases.

The case involves a 68-year-old woman residing in Shau Kei Wan whose symptoms began with joint pain on Monday followed by fever and rash on Tuesday.

According to authorities, she has no travel history in the two months preceding illness and her residence and usual activity areas do not overlap with those of the earlier cases.

Professor Jasper Chan Fuk-woo of the University of Hong Kong’s microbiology department explained that “based on the epidemiological investigation findings released so far, this new case likely represents a new source of infection not linked to the previous three local cases.” He added that genomic analysis of the virus strain should shed further light and warned that the discovery “raises concerns of undetected ongoing transmission chains.”

This development follows earlier local infections recorded in October involving residents of Fung Tak Estate in Wong Tai Sin, where genomic data showed a shared strain.

The city’s public-health agency, the Centre for Health Protection (CHP), has designated nearby residential blocks within a 200-metre radius of the earlier cluster for enhanced mosquito-control measures and urged residents to seek medical advice if they experience fever, rash or joint pain.

The new case adds complexity to Hong Kong’s vector-borne-disease monitoring, especially given the presence of the Aedes albopictus mosquito — a known carrier of the chikungunya virus.

The absence of a clear epidemiological link suggests either an unidentified imported case acted as the source or local circulation has reached a second nidus.

In response, authorities are intensifying mosquito-control operations, including fogging, removal of standing water, and community outreach.

They are also appealing to the public to apply insect repellent, cover up during peak mosquito hours, and eliminate potential breeding sites around homes.

At the same time, health professionals have been advised to consider chikungunya testing for patients presenting with compatible symptoms even without travel history.

While the virus is rarely fatal, it can cause prolonged joint pain, especially among older adults or those with chronic conditions.

The city’s health-care system is prepared for monitoring and containment, but experts say vigilance remains critical as the nature of the fourth case introduces uncertainty into the containment picture.