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Eur J Epidemiol. 2020 Feb 11. doi: 10.1007/s10654-020-00611-w. [Epub ahead of print]

Are infectious diseases risk factors for sarcoidosis or a result of reverse causation? Findings from a population-based nested case-control study.

Author information

1
Clinical Epidemiology Division, Department of Medicine Solna, Karolinska Institutet, Karolinska University Hospital, Eugeniahemmet T2, 171 76, Stockholm, Sweden. marios.rossides@ki.se.
2
Respiratory Medicine Division, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden.
3
Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden.
4
Respiratory Medicine, Theme Inflammation and Infection, Karolinska University Hospital, Stockholm, Sweden.
5
Clinical Epidemiology Division, Department of Medicine Solna, Karolinska Institutet, Karolinska University Hospital, Eugeniahemmet T2, 171 76, Stockholm, Sweden.
6
Rheumatology, Theme Inflammation and Infection, Karolinska University Hospital, Stockholm, Sweden.

Abstract

Findings from molecular studies suggesting that several infectious agents cause sarcoidosis are intriguing yet conflicting and likely biased due to their cross-sectional design. As done in other inflammatory diseases to overcome this issue, prospectively-collected register data could be used, but reverse causation is a threat when the onset of disease is difficult to establish. We investigated the association between infectious diseases and sarcoidosis to understand if they are etiologically related. We conducted a nested case-control study (2009-2013) using incident sarcoidosis cases from the Swedish National Patient Register (n = 4075) and matched general population controls (n = 40,688). Infectious disease was defined using inpatient/outpatient visits and/or antimicrobial dispensations starting 3 years before diagnosis/matching. Adjusted odds ratios (aOR) of sarcoidosis were estimated using conditional logistic regression and tested for robustness assuming the presence of reverse causation bias. The aOR of sarcoidosis associated with history of infectious disease was 1.19 (95% confidence interval [CI] 1.09, 1.29; 21% vs. 16% exposed cases and controls, respectively). Upper respiratory and ocular infections conferred the highest OR. Findings were similar when we altered the infection definition or varied the infection-sarcoidosis latency period (1-7 years). In bias analyses assuming one in 10 infections occurred because of preclinical sarcoidosis, the observed association was completely attenuated (aOR 1.02; 95% CI 0.90, 1.15). Our findings, likely induced by reverse causation due to preclinical sarcoidosis, do not support the hypothesis that common symptomatic infectious diseases are etiologically linked to sarcoidosis. Caution for reverse causation bias is required when the real disease onset is unknown.

KEYWORDS:

Case–control study; Etiology; Infection; Reverse causation; Sarcoidosis

PMID:
32048110
DOI:
10.1007/s10654-020-00611-w

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