2017, the year of Legionella pneumophila

Maybe you weren’t aware, but 2017 was the year of a variety of animals, plants and mushrooms. Bird-watchers had the year of the cuckoo, the German Naturheilverein NHV Theophrastus had the year of the daisy, the Dutch Mammal Society had the year of the serotine bat, and mycologists had the year of the beefsteak polypore mushroom. Often the purpose of naming a species of the year is to generate extra attention for endangered species, as a way of emphasising the importance of biodiversity.

What strikes me about lists of this kind is that they don’t include bacterial species, even if bacteria play an indispensable role in nature and bacterial biodiversity far exceeds that of the eukaryotes. It wouldn’t be difficult to think of bacterial species that could be the focus of more attention in 2018 – species that represent a threat to public health for instance. Good candidates in this category would include Vibrio cholerae or Salmonella typhi, species that are still responsible for the death of too many people worldwide. One could also choose bacterial species that have been named after renowned microbiologists, partly as a way of commemorating them. Streptomyces leeuwenhoekii or Beijerinckia indica would be good candidates in the Netherlands. We could also of course draw attention to bacterial species that seem to be struggling.  I’m thinking for example of Clostridium lactatifermentans, a bacterial species that I isolated, characterised and was allowed to name in 2002, but about which very little has been heard since.

In retrospect, we could actually declare 2017 the year of Legionella pneumophila. Although the exact number of people in the Netherlands who fell ill because of Legionella pneumophila is still unknown, it is already clear that the reported cases of legionellosis will exceed 500. This represents a record number since RIVM began recording annual cases of the disease. This might be news to you, because cases of legionellosis caused by L. pneumophila no longer attract much public attention. Things were different at the beginning of the century, when, following the big legionellosis outbreak in Bovenkarspel, both government and media paid a great deal of attention to legionellosis. This meant that money was available for research. KWR’s contribution to this effort included demonstrating that the organism multiplied in single-cell organisms, which are present in water-related biofilms. We also showed that cooling towers frequently offer more favourable environments for L. pneumophila than water systems. Surprisingly enough, the government has targeted legislation and enforcement primarily at water systems. Building managers invest large amounts of euros every year to comply with the legislation, but, considering the high number of legionellosis cases in 2017, the intended results haven’t been achieved.

Even if regulations for cooling towers are implemented, a number of the towers will always escape attention, simply because we don’t have a good idea of where they all are. Moreover, the effectiveness of specific control measures is a lot less clear when it comes to cooling towers. It would therefore not surprise me if cooling towers turn out to be one of the main sources of the L. pneumophila infecting Dutch patients. In light of the recent increase in the number of people falling ill with legionellosis in the Netherlands, one might expect that the government would be actively working on the matter. But the opposite seems to be the case, because, while KWR frequently conducted research projects on L. pneumophila for the government in the past, this activity has completely dried up over the last few years; a trend confirmed by fellow research institutes. Although it is absolutely terrible for those who became ill – or even died – because of L. pneumophila last year, a positive consequence of the 2017 record year might be to wake up the government. This wake-up call could then hopefully lead to a joint research and action plan aimed at determining the precise role played by cooling towers in the spread of L. pneumophila, gaining a better understanding of the microbial ecology of L. pneumophila in cooling towers, and defining and testing effective control measures for L. pneumophila in cooling towers. It would actually be wonderful if 2018 were not also to become the year of Legionella pneumophila: this would clear the way to declare 2018 the year of Clostridium lactatifermentans.