Diphtheria numbers in the Northern Territory reportedly surged weeks before a public health alert was issued, according to leaked NT Health data.
Unlike some states which provide public online data about disease case numbers and locations, NT Health does not release specific details publicly.
But a document the department shared with service providers this week was leaked to the ABC, which revealed some of its contents to the public today.
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The data reportedly showed multiple cases of diphtheria were being recorded across Darwin, the Top End and the Katherine region from late February.
A public health alert about the outbreak, which is now Australia's worst on record, was not issued by NT Health until the end of March.
An NT Health spokesperson told nine.com.au the department "implemented a timely and proportionate public health response" to the ongoing outbreak.
"The response has included the identification and treatment of all cases and close contacts including vaccination where indicated," they said.
"In addition, NT Health has commenced a vaccination campaign aimed at preventing severe illness and reducing transmission within the community."
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Vaccination clinics have been set up across the NT and more than 10,000 diphtheria-containing vaccines have been administered over the past seven weeks.
Weekly case numbers have also been declining through the month of May.
"NT Health continues to closely monitor the situation and will adjust its public health response as required to protect the health of Territorians," the spokesperson said.
NT Chief Health Officer Dr Paul Burgess confirmed earlier this week that the outbreak had spread across all five regions of the NT.
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Diphtheria is highly contagious and can cause severe illness and death.
Even with treatment, one in 10 patients die, according to the CDC.
More than 250 diphtheria cases have been reported to the Centre for Disease Control (CDC) already, about 60 per cent of them from the NT.
One death has been recorded so far.
Earlier this month, Federal Health Minister Mark Butler announced the federal government is throwing millions at controlling the outbreak.
A spokesperson told nine.com.au the outbreak is of deep concern to the Government.
"We are working closely with affected jurisdictions to ensure a coordinated and effective national response to the diphtheria outbreak," they said.
"Within a matter of days of receiving a request for help from the NT Government, we started sending additional doses of vaccines to the Territory.
"This package is focused on increasing vaccination coverage, strengthening the health workforce in the NT, and supporting community-led responses in affected regions."
