Legionnaire’s cases triple the amount thought

Researchers find triple as many Legionnaire’s cases as
previously reported.

The first New Zealand-wide study of
the burden of Legionnaire’s disease has found triple the
number of cases of this form of pneumonia than previously
reported.

The study, led by University of Otago,
Christchurch Professor David Murdoch, has just been
published in the Lancet Infectious Diseases. It gives
the first accurate picture of the burden of the disease in
New Zealand, but has international implications as few
places routinely test for the potentially deadly – and
preventable - bacteria.

The researchers arranged for
people hospitalised with pneumonia from almost all of New
Zealand during one calendar year to have a specialised test
that detects legionella bacteria. Three times the number of
cases were diagnosed compared with the average number of
cases confirmed over each of the previous three
years.

Specifically, the researchers found:

• About
two-thirds of cases were admitted to hospital during winter
and spring.

• Almost 60% of patients were aged over
65.

• Nearly a third of confirmed cases lived in more
socio-economically deprived areas.

• Almost 80% of
patients had been hospitalised at some time over the
previous five years, but fewer than half (41%) had been
hospitalised for respiratory disease.

• High rates of
the disease in areas which had previously reported low
numbers of cases. Notably, the Bay of Plenty District Health
Board area (more than 8 cases per 100,000 people) and the
Hawkes Bay and the Waitemata (which both had between 6 and 8
cases per 100,000). Canterbury also had rates of between 6
and 8 cases per 100,000 but had previously recorded
reasonably high numbers of cases.

Professor Murdoch, a
clinical microbiologist and researcher, says a special test
called the polymerase chain reaction (PCR) is the best way
to diagnose Legionnaires’ disease as chest x-rays or other
tests cannot differentiate between this and other forms of
pneumonia. The disease requires different treatments from
other types of pneumonia. The sooner the infection is
treated with bacteria-specific medication, the better the
prognosis, he says.

“This research shows the incidence
of Legionnaires’ disease in New Zealand is much higher
than previously identified. Indeed, we have the highest
reported incidence in the world. The research also supports
the routine use of the PCR test to detect and ensure access
to appropriate treatments,’’ Professor Murdoch
says.

The results are relevant to other countries as the
bacteria causing Legionnaires’ disease is present
internationally but few countries have routine testing in
place, Professor Murdoch says.

The study identified the
most common form of bacteria causing the disease in New
Zealanders was Legionella longbeachae (in 63% of
cases). This strain is found in soil and composted plant
material, and people at greatest risk are those involved in
gardening activities.

To get their results, the research
team tested all respiratory samples from patients with
pneumonia admitted to any of the 20 participating hospitals
between May 2015 and May 2016. During the year a total of
238 cases were identified, or 5.4 cases per 100,000 New
Zealanders. This was three times the rate expected based on
the number of people diagnosed in the preceding three years.
Of the 238 cases, 15 died within 90 days of diagnosis and 38
cases required treatment in an intensive care unit (ICU).

Professor Murdoch says the research was possible because
of the involvement of staff and laboratories from 20
hospitals and 17 different District Health Boards. It is
unusual for this degree of collaboration on research
projects, he said.

The research was funded by the Health
Research Council of New Zealand (HRC).

HRC chief executive
Professor Kath McPherson says the study demonstrates the
vital importance of accurate data. “Without robust data,
we can completely underestimate the extent of a problem and
make uninformed decisions, and in health that can have
extremely negative consequences. It is very pleasing to see
this huge collaborative effort result in definitive findings
that should inform practice and policy throughout our
country and internationally where such work has not been
done.”

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