Objective To collect the background date of microbial contamination of the air conditioning systems of metro line 2 before operation for future monitoring.
Methods The central air conditioning systems of 16 metro stations were monitored for 3 consecutive days, twice a day, morning and afternoon. The monitoring indicators included total bacterial count, β-hemolytic streptococcus, and total fungi on the inner surface of duct and in wind duct, as well as Legionella pneumophila in cooling and condensate water.
Results The qualification rates on the inner surface of duct and in wind duct were 44.7% and 59.4% for the total fungi, and 100.0% and 96.6% for the total bacterial count, respectively. No β-hemolytic streptococcus was detected. Of the 32 samples of cooling water and condensate water detected, the positive rate of Legionella pneumophila were 28.1% and 0%, respectively (P<0.05). The mean of total fungi in wind duct of station concourses and platforms were 413 cfu/m3 and 625 cfu/m3, respectively (P<0.01), and those on the inner surface of duct were 620 cfu/m3 and 527 cfu/m3, respectively (P<0.01). There were no statistical differences in other indicators between platforms and concourses (P>0.05).
Conclusion The bacteria levels in central air conditioning systems of metro line 2 in Xi'an are well within the accepted limits, but fungi contamination is found. It is suggested that related departments strengthen surveillance on the air conditioning systems of metro stations.
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