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Volume 29, Number 6—June 2023
Research

Increased Incidence of Legionellosis after Improved Diagnostic Methods, New Zealand, 2000–2020

Frances F. GrahamComments to Author , David Harte, Jane Zhang, Caroline Fyfe, and Michael.G. Baker
Author affiliations: University of Otago, Wellington, New Zealand (F.F. Graham, J. Zhang, C. Fyle, M.G. Baker); Environmental Science and Research, Wellington (D. Harte)

Main Article

Table 1

Characteristics of notified case-patients by age group, sex, ethnicity, and Legionella species, New Zealand, 2000–2020*

Category 2000–2009
 2010–2020
 Comparison of 2 periods, IRR (95% CI)
No. cases Crude rate ASR† (95% CI) IRR 
(95% CI) No. cases Crude rate ASR† (95% CI) IRR 
(95% CI)
Age group, y
Total 643 1.6 1.5
(1.4–1.6)		 NA 1,985 3.9 3.8
(3.6–3.9)		 NA 2.5 (2.3–2.7)
<1–39 46 0.2 NA Referent 99 0.4 NA Referent 1.7 (1.2–2.9)
40–59 219 1.9 NA 9.1
(6.6–12.5)		 619 5.0 NA 12.8
(10.3–15.8)		 2.5 (2.1–2.9)
>60
 378
 4.5
 NA
21.9
(16.1–29.7)
1,267
 11.8
 NA
32.8
(26.7–40.2)
2.6 (2.3–2.9)
Sex
M 383 1.9 1.9
(1.7–2.11)		 1.7
(1.4–2.0)		 1,265 5.0 5.0
(4.7–5.2)		 1.9
(1.8–2.1)		 2.6 (2.3–2. 9)
F 254 1.2 1.1
(1.0–1.3)		 Referent 720 2.7 3.0
(2.4–2.8)		 Referent 2.3 (2.0–2.6)
Unknown
 6
 NA
0
 NA
Ethnicity
European 517 2.3 2.1
(1.9–2.3)		 Referent 1,620 4.5 3.9
(3.7–4.1)		 Referent 1.85 (1.67–2.04)
Māori 27 0.5 0.7
(0.4–1.1)		 0.35
(0.22–0.55)		 149 1.7 2.8
(1.4–3.3)		 0.73
(0.61–0.88)		 3.89 (2.42–6.25)
Pacific Peoples 13 0.6 0.7
(0.3–1.1)		 0.32
(0.17–0.58)		 72 1.7 3.1
(2.3–3.9)		 0.80
(0.62–1.03)		 4.63 (2.42–8.88)
Other 17 0.2 0.2
(0.1–0.4)		 0.11
(0.07–0.19)		 93 1.1 1.7
(1.4–2.1)		 0.45
(0.36–0.56)		 7.46 (4.31–12.9)
Unknown
 69
 NA
51
 NA
Laboratory status
Confirmed 537 1.3 0.9
(0.8–0.9)		 Referent 1,700 3.3 2.4
(2.2–2.5)		 Referent 2.7 (2.5–3.0)
Probable
 106
 0.2
 0.2
(0.1–0.2)
 0.2
(0.2–0.23)
285
 0.6
 0.4
(0.3–0.4)
 0.2
(0.1–0.2)
2.2 (1.7–2.7)
L. pneumophila
Total 256 6.2 NA NA 527 11.2 NA NA 1.80 (1.57–1.94)
<1–39 9 0.3 Referent 58 0.8 Referent 2.67 (2.31–2.86)
40–59 58 1.0 1.41
(0.97–1.73)		 196 2.9 2.85
(2.19–3.12)		 2.90 (2.50–3.04)
>60
 189
 3.2
13.6
(9.42–16.5)
273
 4.9
5.15
(3.99–5.63)
1.53 (1.33–1.88)
L. longbeachae
Total 161 3.9 NA NA 1,062 22.6 NA NA 5.79 (5.49–6.12)
1–39 5 0.1 Referent 39 0.6 Referent 2.00 (1.96–2.29)
40–59 56 1.0 2.60
(1.70–3.26)		 284 3.8 1.76
(1.41–1.85)		 3.80 (3.68–3.96)
>60
 98
 2.4
7.50
(5.00–9.42)
739
 14.6
11.02
(8.86–11.51)
6.10 (6.26–6.67)
Other species
Total 87 2.1 NA NA 251 5.3 NA NA 2.52 (2.16–2.89)
<1–39 11 0.1 Referent 50 0.7 Referent 7.00 (6.43–7.69)
40–59 35 0.5 3.24
(1.94–4.56)		 79 1.2 2.21
(1.55–2.64)		 2.40 (1.90–2.50)
>60 41 0.9 4.30
(2.58–5.99)		 122 2.3 4.56
(3.26–5.34)		 2.56 (2.35–2.83)
Unknown 139 NA 145 NA

*Crude rate is cases per 100,000 population. ASR, age-standardized rate; IRR, incidence rate ratio; NA, not applicable. †Age standardized to the New Zealand population age structure at the 2013 census.

Main Article

Page created: April 12, 2023
Page updated: May 17, 2023
Page reviewed: May 17, 2023
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