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out 100% sampling of three large batches and, as will be seen from
the appendix, the results revealed the extent of the contamination.
The second meeting of riparian medical officers, held on 12th
July 1961, was called at my request and this time I insisted that a
Ministry of Health representative be present. The results of all the
tests as listed in the appendix were presented by me and the question
of the disposal of 130 tons of cheese was discussed. I strongly resisted
a proposal that all this cheese should be released for processing at
5% dilution. Following considerable further discussion it was
move by the Ministry of Health representative that cheese with
counts between 200,000,000 and 600,000,000 should be considered
as unfit for human consumption but that cheese with counts of up to
200,000,000 should be released for dilution to 5% in processing. This
was a level which it was suggested should produce a safety margin by
dilution. In any processed cheese thus diluted there would be in the
heaviest contaminated cheese the possibility of toxin from a count of
10.000,000 (5% of 200,000.000). Already a variety of brands of
cheese had been tasted with counts up to 60,000,000 without ill
effect; although the heat treatment of processing would kill the staphylococci but would not affect the toxins; it was held, however, that
the 5 % dilution would lower the level of toxin to a safe degree.
Preventive Measures
Obviously, this soultion could not be regarded as desirable for
the future, and it was essential to ensure that future supplies of
cheese, either Ist or 2nd grade, were as free from coagulase-positive
staphylococci as possible.
The New Zealanders, following our advice that milk for cheese
making should be fully pasteurised, rapidly introduced legislation
for its compulsory effective pasteurisation (161°F for 15 secs.).
Also all crates and boxes of 2nd grade cheese were to be marked
"For Processing Only" and directed to cheese processing factories
only. Further, bacteriological sampling of cheese would be carried
out in New Zealand to cover the production and marketing of the
cheese. A provisional standard was introduced for future consignments
of 2nd grade cheese, namely 500,000 coagulase-positive
staphylococci per gram, beyond which importation would not be
allowed.
Results
The bacteriological examination of 2nd grade cheese produced
after the introduction of the new regulations in New Zealand showed
an immense improvement with very low counts or absence of coagulase-positive
staphylococci.
Comment
(i) 2nd grade cheese, from whatever source, can be a dangerous
commodity. It should only be released for processing (heat treatment
and dilution); and then only if made from pasteurised milk.
The production, development and storage should be covered by
bacteriological sampling.