12th May 2017, Volume 130 Number 1455

Frances Graham, David Harte

Legionellosis is an important notifiable disease often causing sporadic community-acquired pneumonia in New Zealand.1 The predominant Legionella species responsible for disease are L. pneumophila and L. longbeachae; collectively contributing to…

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Legionella bacteria is ubiquitous in the environment. This study set out to expand our understanding of the environmental exposure risks to Legionella and whether seemingly unrelated environmental factors, such as aerosolised liquefaction-affected soil resulting from the Christchurch earthquakes had the potential to impact on disease prevalence. Liquefaction-affected soil could not contribute directly to the observed increase in legionellosis cases after the earthquakes due to its inability to support growth and survival of the Legionella bacteria. Chemical and size analysis of the liquefaction-affected soil showed it consisted of >65%. Silica. The authors propose that inhalation of earthquake associated airborne liquefaction-affected soil can damage lung tissue and cause inflammation. Inflammation and damage could allow opportunistic pathogens, such as Legionella bacteria, to more successfully infect the human host.



To investigate a possible link between liquefaction dust exposure and the noticeable increase in legionellosis cases in response to major earthquakes in 2010 and 2011 that resulted in widespread soil disturbance (liquefaction) in parts of Christchurch, New Zealand.


We culture tested liquefaction-affected soil for Legionella spp. in the six months following the first earthquake in 2010. Thirty silt samples were collected randomly from locations within Christchurch’s metropolitan area that were affected by liquefaction. The samples were tested to determine the presence of Legionella using qualitative and quantitative methods. Liquefaction-affected soil samples from three sites were further subjected to particle size distribution analysis and determination of major oxides. A controlled field study was established using six silt samples and one control (commercial compost), seeded with a wild-type strain of Legionella bozemanae serogroup (sg) 1 and persistence monitored over a 60-day period by culturing for the presence of Legionella. Dry matter determinations were undertaken so that total Legionella could be calculated on a dry weight basis.


Legionella bacteria were undetectable after day one in the silt samples. However, L. bozemanae sg1 was detected in the control sample for the entire study period.


This study showed that the liquefaction-affected soil could not contribute directly to the observed increase in legionellosis cases after the earthquakes due to its inability to support growth and survival of the Legionella bacteria.

Author Information

Frances F Graham, Department of Public Health, University of Otago, Wellington; Environmental Health, Regulation Health Protection and Emergency Management Division, Department of Health and Human Services, Melbourne, Australia; David JG Harte, Legionella Reference Laboratory, Institute of Environmental Science and Research, Porirua, Wellington.


Caroline Fyfe, research assistant, Centre for Public Health Research, Massey University, assisted in the construction of the map using ArcGIS. Alice Graham assisted in the collection of liquefaction samples. Dr Richard Wysoczanski (NIWA), Dr Scott Nodder (NIWA) and Lisa Northcote (NIWA) assisted in the XRF and particle grain-size analyses. Teresa Aberkane, Environment Canterbury assisted in the provision of air pollution data Frances Graham’s PhD and this research were supported by the New Zealand Ministry of Health. The analyses, conclusions, opinions and statements expressed herein are those of the authors and do not necessarily represent the views or policy of Environment Canterbury or the New Zealand Ministry of Health. Environment Canterbury and the Ministry of Health do not assume any liability or responsibility for use of or reliance on the contents of this article.


Frances Graham, Department of Public Health, University of Otago, PO Box 7343, Wellington 6242.

Correspondence Email


Competing Interests



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