Epidemiol. Infect. (2014), 142, 1695–1707. © Cambridge University Press 2013 doi:10.1017/S0950268813002768

Risk factors for susceptibility to varicella in newly arrived adult migrants in Canada

C. GREENAWAY 1 , 2 , 3 *, J. F. BOIVIN 2 , 3 , S. CNOSSEN 2 , C. ROSSI 3 , B. TAPIERO 4 , K. SCHWARTZMAN 5 , S. OLSON 6 AND M. MILLER 1 1

Division of Infectious Diseases, Jewish General Hospital, McGill University, Montreal, Canada Lady Davis Research Institute, Jewish General Hospital, Montreal, Canada 3 Department of Epidemiology and Biostatistics, McGill University, Montreal, Canada 4 Pediatric Infectious Diseases Division, Department of Pediatrics, CHU Sainte-Justine, University of Montreal, Montreal, Canada 5 Respiratory Epidemiology and Clinical Research Unit, Montreal Chest Institute, McGill University, Montreal, Canada 6 Department of Geography, McGill University, Montreal Canada 2

Received 25 April 2013; Final revision 12 September 2013; Accepted 7 October 2013; first published online 1 November 2013 SUMMARY Varicella occurs at an older age in tropical compared to cold climates. Migrants from tropical countries provide the opportunity to gain insights into observed global differences in varicella epidemiology. Severity of varicella increases with age thus, description of risk factors for varicella susceptibility will identify those who would benefit most from vaccination. A total of 1480 migrants, with a mean age of 32 years, were recruited in the pre-vaccination period (2002–2004) in Montreal, Canada. A questionnaire was administered and serum varicella antibodies were measured. Overall 6% were susceptible and ranged from 0·8% to 14·1% in subgroups. Risk factors for susceptibility were younger age, recent arrival, and originating from a tropical country. This could be modified by conditions that increased the probability of person-to-person spread of varicella through direct contact in source countries such as larger community size or household crowding. Many new young adult migrants would benefit from targeted varicella vaccination programmes. Key words: Immigrant, migrant, predictors of susceptibility, refugee, varicella.

I N T RO D U C T I O N Varicella seroprevalence studies conducted in countries with tropical or equatorial climates (warm and humid year round) have found that a significant proportion (∼20%) of adolescent and young adults are susceptible to varicella compared to 250 000 population) or lower (425000 population) [22]. The income level was self-reported as low, middle, or high in comparison to other persons in the same community of origin. Large households in the community of origin were defined as having >7

people living in a household and smaller households as having 47 people. This cut-off was chosen because the mean number of people living in a household in our study population was 6·7 ± 3·2 people. The term migrant used throughout the paper refers to foreignborn persons who are permanent or non-permanent residents of Canada [17]. Refugee status was dichotomized as refugees (included refugee or refugee claimant) vs. all others (Table 1).

Serological testing Blood samples were obtained from all participants for serological testing. Varicella immunoglobin G (IgG) antibodies were measured using the Dade Behring (Deerfield, USA) ELISA assay. Results were classified

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Table 2. Susceptibility to varicella, univariate, and multivariable logistic regression Variable

Total, n

Susceptible % (95% CI)

Univariate OR (95% CI)

Multivariable aOR (95% CI)

Overall

1480

5·9 (4·7–7·1)

–

–

Sex Male Female

490 990

6·7 (4·5–8·9) 5·5 (4·1–6·9)

1·3 (0·8–2·0) 1·0

1·5 (0·9–2·5) 1·0

Age (years) 250 000

612 811

8·2 (6·0–10·4) 4·2 (2·8–5·6)

2·0 (1·3–3·2)* 1·0

1·9 (1·2–3·1)* 1·0

Refugee status Refugee Non-refugee

723 757

7·1 (5·2–9·0) 4·8 (3·3–6·3)

1·5 (1·0–2·4)* 1·0

1·4 (0·9–2·2) 1·0

1025 448

6·9 (5·3–8·5) 3·6 (1·9–5·3)

2·0 (1·2–3·5)* 1·0

2·1 (1·2–3·8)* 1·0

Climate Tropical rainforest Tropical monsoon Tropical savannah Temperate Arid/cold/polar

64 160 351 477 407

14·1 (5·6–22·6) 7·5 (3·4–11·6) 7·4 (4·7–10·1) 5·7 (3·6–7·8) 2·5 (1·0–4·0)

6·5 3·2 3·2 2·4 1·0

(2·5–16·7)* (1·4–7·6)* (1·5–6·7)* (1·1–5·0)*

5·4 2·8 3·1 2·4 1·0

Latitude (degrees) >0 to 410 N or S >10 to 420 N or S >20 to 430 N or S >30 to 440 N or S >40 N or S

330 352 211 390 176

6·7 (4·8–8·6) 6·3 (4·5–8·1) 6·6 (4·2–9·0) 4·6 (3·1–6·1) 4·5 (2·3–6·7)

1·5 1·4 1·5 1·0 1·0

(0·7–3·4) (0·6–3·2) (0·6–3·6) (0·4–2·4)

– – – – –

Region of origin South Asia Latin America or Caribbean East Asia and the Pacific Eastern Europe and Central Asia Sub-Saharan Africa North Africa or Middle East

318 356 220 157 256 173

10·1 (6·8–13·4) 6·2 (3·7–8·7) 4·5 (1·8–7·2) 4·5 (1·3–7·7) 3·5 (1·3–5·8) 4·0 (1·1–6·9)

2·7 1·6 1·1 1·1 0·9 1·0

(1·2–6·2)* (0·7–3·7) (0·4–3·0) (0·4–3·2) (0·3–2·4)

– – – – – –

Island vs. non-island Island Non-Island

177 1303

10·7 (6·1–15·3) 5·2 (4·0–6·4)

2·2 (1·3–3·7)* 1·0

– –

Father farmer Yes No

219 1248

6·9 (3·5–10·3) 5·6 (4·3–6·9)

1·2 (0·7–2·2) 1·0

– –

Subject farmer Yes No

64 1414

7·8 (1·2–14·4) 5·8 (4·6–7·0)

1·4 (0·5–3·5) 1·0

– –

Time since arrival in Canada (years) 7

(2·0–14·7)* (1·2–6·9)* (1·4–6·6)* (1·1–5·0)*

Susceptibility to varicella in migrants

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Table 2 (cont.) Variable

Total, n

Susceptible % (95% CI)

Univariate OR (95% CI)

Multivariable aOR (95% CI)

Income level Lower Middle Upper

93 1242 142

9·7 (3·7–15·7) 6·0 (4·7–7·3) 2·8 (0·1–5·5)

3·7 (1·1–12·4)* 2·2 (0·8–6·1) 1·0

– – –

OR, Odds ratio; aOR, adjusted odds ratio; CI, confidence interval. * Indicates estimates that were statistically significant with a P value 0·20 were considered positive, OD values