Final Clarity on Mosquito Prevention for Contractors and Construction Sites

The recent judgement in HCMA597/2019 (handed down on 23 September 2020) contains significant guidance for the construction industry and provides confirmation of what this writer has always believed to be the case, in respect of the steps and measures required to prevent mosquito breeding at law; in order to mount an effective defence to a prosecution under s.27(3) of the Public Health and Municipal Services Ordinance, Cap. 132.

Prosecutors have historically relied upon a slightly inconclusive case, which this writer was involved in, HKSAR v Kier Hong Kong Limited, HCMA 845/2006, where it was held:

19. Even if the offence is one of strict liability and the defence of honest mistake upon reasonable grounds is available to a Defendant in certain circumstances, I am satisfied that such a defence is not available where the prohibited circumstances are the result of the negligent acts or omissions of a person or persons to whom the appellant has entrusted the task of ensuring that the law is complied with.

The “even if” part of the judgement unfortunately did not confirm the status of the offence, and the case also involved a very fact specific decision. Failure, by an individual as was touched on, is something that the courts have been reluctant to allow companies to rely upon once admitted; even if it remains open as a defence.

The current case however provides useful guidance and final confirmation in respect of key matters that have been misunderstood or perhaps even ignored to date.

The offence involved is one of strict liability and the common law defence is applicable is now clear:

The offence is one of strict liability. The core issue at the trial was whether the appellant had made out the common law defence of honest and mistaken belief upon reasonable grounds in its failure to comply with the legislative requirement.” (Para 5 of Judgment in HCMA 597/2019)

The burden of proving what was done in order to meet the requirements of the legislation, and government guides however remains on a defendant; assuming all the core elements of the offence are proven by a prosecutor. The prosecution cannot however sit back and do no more than simply advance a finding of larvae or pupae in order to guarantee a conviction; as all responsible contractors or site operators will take mosquito suppression measures, and can always lead evidence of such.

Finally, and importantly, what a company may form as an opinion or have as a state of mind, based upon past actions, inspections, visits and protocols deployed, together with their own findings, is very important. In order to form an honestly held belief in respect of compliance, one must hold and be able to prove that to be the case with good and sufficient reasons being given for holding the belief. On this the ruling added:

There was unchallenged evidence that the appellant did hold such honest belief for good reason that the anti-mosquito breeding water control measures were being conducted and the HKSAR Government published recommendations were being complied with and exceeded. The magistrate did not reject the appellant’s belief. There was no evidence that the reasons for forming of the belief were in anyway flawed or inadequate.” (Para 35 of the Judgment in HCMA 597/2019)

This case featured a backdrop of literally dozens of full compliance visits being undertaken by the Government, extensive suppression measures adopted by the contractor and an acceptance by the prosecution’s own expert witness that one could never possibly obviate all larvae or pupae, at any location, given the known development life cycle. It was an impossible threshold; for anybody to create a “zero larvae” or a “zero pupae” situation on an open site at all times, even by following the protocols, recommendations and guidance of the Government.

Finally, we have some certainty and predictability in respect of the law on a topic that has vexed trial courts for far too long.

Adrian J. Halkes, Barrister at Law


Chairman of Pro Bono Committee