[Swarms of starlings in Basel: a natural phenomenon, a nuisance or a health risk?]

A Natural Phenomenon, Molestation or a Health Risk? For the last two decades an avenue in the centre of Basel (Altrheinweg, Klybeckquartier) is known as site for overnight accommodation and assembly of starlings (Sturnus vulgaris) during autumn. The nightly visitors cause an immense contamination that directly affects a nursery and a primary school. The aim of the present study was the evaluation of the health risk for the population due to the starlings' droppings, particularly for the children from the nursery school. Between August and December of the years 1995 and 1996 the population of starlings was observed, the contamination of the area with faeces was quantified, the presence of microorganisms in the faeces was determined and the contamination of the soil from the Altrheinweg was compared with that from other avenues and parks. Furthermore, the children attending the nursery school were monitored for possible infections due to the birds' droppings. In mid-October, when the population of starlings reached their maximum of about 15,000 birds, 1053 defecations per night and square metre were counted on an average in 1995 and 1821 in 1996. The microbiological analysis of the starlings' faeces showed a high contamination with Campylobacter spp. (1995: 95.5%; 1996: 100%), L. monocytogenes (1995: 36.5%; 1996: 26.7%) and C. psittaci (1995: 40.5%), a lower contamination with Salmonella spp. (1995: 1.0%), S. aureus (1995: 2.0%), Y. enterocolitica (1995: 1.5%) and Y. pseudotuberculosis (1995: 1.0%). Mycotic and parasitic human pathogens were not found. The contamination of the soil from the Altrheinweg with Campylobacter spp. and L. monocytogenes was significantly greater than that of the other avenues and parks in Basel. However, the investigations conducted by the school medical service showed that no infections among the children attending the nursery school could be correlated to the presence of the starlings. Even if the heavy contamination of the area with droppings of starlings presents a potential health risk, a continuous or systematic transmission of infectious agents seems rather improbable due to the contamination-avoiding behaviour of the children, the characteristics of the microorganisms involved and the climatic conditions in autumn. This situation showed however not reduce our awareness of such a potential health risk.