  We propose a novel approach and an empirical procedure to test direct
contagion of growth rate in a trade credit network of firms. Our hypotheses are
that the use of trade credit contributes to contagion (from many customers to a
single supplier - "many to one" contagion) and amplification (through their
interaction with the macrocopic variables, such as interest rate) of growth
rate. In this paper we test the contagion hypothesis, measuring empirically the
mesoscopic "many-to-one" effect. The effect of amplification has been dealt
with in another paper.
  Our empirical analysis is based on the delayed payments between trading
partners across many different industrial sectors, intermediated by a large
Italian bank during the year 2007. The data is used to create a weighted and
directed trade credit network. Assuming that the linkages are static, we look
at the dynamics of the nodes/firms. On the ratio of the 2007 trade credit in
Sales and Purchases items on the profit and loss statements, we estimate the
trade credit in 2006 and 2008.
  Applying the "many to one" approach we compare such predicted growth of trade
(demand) aggregated per supplier, and compare it with the real growth of Sales
of the supplier. We analyze the correlation of these two growth rates over two
yearly periods, 2007/2006 and 2008/2007, and in this way we test our contagion
hypotheses. We could not find strong correlations between the predicted and the
actual growth rates. We provide an evidence of contagion only in restricted
sub-groups of our network, and not in the whole network. We do find a strong
macroscopic effect of the crisis, indicated by a coincident negative drift in
the growth of sales of nearly all the firms in our sample.
