Risk of respiratory infection in patients with plaque psoriasis
Authors: Axel Svedbom, Lotus Mallbris, Mona Ståhle
Journal: Journal of the American Academy of Dermatology (2021)

To the Editor: Understanding the risk of respiratory infection in psoriasis and the impact of immunosuppressive treatment is important to inform preventive measures for COVID-19. Therefore, we report data on respiratory infection in patients with psoriasis from a study linking an inception cohort1Mallbris L. Larsson P. Bergqvist S. Vingard E. Granath F. Stahle M. Psoriasis phenotype at disease onset: clinical characterization of 400 adult cases.J Invest Dermatol. 2005; 124: 499-504Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar to population-based health care registers on outpatient care, inpatient care (The National Patient Register2Ludvigsson J.F. Andersson E. Ekbom A. et al.External review and validation of the Swedish national inpatient register.BMC Public Health. 2011; 11: 450Crossref PubMed Scopus (3652) Google Scholar), and prescriptions (The Prescribed Drug Register3Wettermark B. Hammar N. Fored C.M. et al.The new Swedish Prescribed Drug Register—opportunities for pharmacoepidemiological research and experience from the first six months.Pharmacoepidemiol Drug Saf. 2007; 16: 726-735Crossref PubMed Scopus (1333) Google Scholar). The Stockholm Psoriasis Cohort enrolled patients with new-onset psoriasis and population controls, predominately in Stockholm, Sweden, between 2001 and 2005.1Mallbris L. Larsson P. Bergqvist S. Vingard E. Granath F. Stahle M. Psoriasis phenotype at disease onset: clinical characterization of 400 adult cases.J Invest Dermatol. 2005; 124: 499-504Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar The study had ethics approval, and participants provided informed consent (Appendix 1 for information on the study; available at https://data.mendeley.com/datasets/vh2k3nvsn9/1). For the analyses at hand, the exposures were mild and moderate-to-severe plaque psoriasis. In a separate analysis, immunosuppressive treatment for psoriasis as observed in the Prescribed Drug Register was a time-dependent exposure. The outcomes in the study were the first respiratory infection after onset from the National Patient Register; and prescriptions of antibiotics and antivirals used to treat respiratory infection from the Prescribed Drug Register (see Supplementary Table I (Table S2.1). Supplementary Table II (Table S2.2), and Supplementary Table III (Table S2.3); available at https://data.mendeley.com/datasets/vh2k3nvsn9/1). Covariates comprised sex, age, and characteristics associated with both respiratory infections and psoriasis for which the standardized mean difference between groups exceeded 0.15. Patients with mild and moderate-to-severe psoriasis were compared with controls. Cox Proportional Hazard models4Cox Regression models and life tables.J R Stat Soc. 1972; 34: 187-220Crossref Google Scholar were used to compare time to first diagnosis, and negative binomial regression models5Lawless J.F. Negative binomial and mixed Poisson regression.Can J Stat. 1987; 15: 209-225Crossref Scopus (772) Google Scholar were used to compare the incidence of prescriptions between groups. We also compared the incidence of prescriptions of antibiotics and antivirals for respiratory infections when patients were treated with immunosuppressive treatment compared with when they were not. In total, 339 patients with mild plaque psoriasis, 187 patients with moderate-to-severe plaque psoriasis, and 835 controls were included. Among the 526 patients, 121 were treated with immunosuppressants. Baseline characteristics are presented in Table I.Table IPatient characteristics∗With the exception of age at indexation, all characteristics were measured at enrolment. of patients and controlsControlsMild psoriasisModerate-to-severe psoriasisSubjects (n)835339187Male sex n (%)482 (42)189 (44)99 (47)Age at index, mean (SD)45 (15)43 (16)†P < .05 versus controls.45 (18)BMI, median (IQR)24 (22, 27)25 (22, 27)25 (22, 29)†P < .05 versus controls.‡Standardized mean difference greater than 0.15 versus controls. Mild psoriasis was defined as PASI below five in the absence of phototherapy and systemics, and moderate-to-severe psoriasis was defined as PASI above five or treatment with phototherapy and systemics.Current smoking n (%)155/827 (19)108/336 (32)†P < .05 versus controls.‡Standardized mean difference greater than 0.15 versus controls. Mild psoriasis was defined as PASI below five in the absence of phototherapy and systemics, and moderate-to-severe psoriasis was defined as PASI above five or treatment with phototherapy and systemics.83/185 (45)‡Standardized mean difference greater than 0.15 versus controls. Mild psoriasis was defined as PASI below five in the absence of phototherapy and systemics, and moderate-to-severe psoriasis was defined as PASI above five or treatment with phototherapy and systemics.§P < .001 versus controls.Frequency of alcohol intake n (%) Never65/819 (8)39/331 (12)38/176 (22) Once per month198/819 (24)73/331 (22)26/176 (15) Two to four times per month317/819 (39)131/331 (40)59/176 (34) Two to three times per week196/819 (24)77/331 (23)38/176 (22) Four time per week or more43/819 (5)11/331 (3)15/176 (9)Comorbidity n (%) Diabetes18/812 (2)13/339 (4)5/187 (3) Neoplasm35/810 (4)17/295 (6)10/147 (7) Stroke6/810 (1)2/298 (1)1/147 (1) Myocardial infarction17/809 (2)5/297 (2)6/147 (4) Asthma80/809 (10)25/295 (8)17/148 (11) Hay fever76/805 (9)30/293 (10)10/148 (7) Thyroid disease32/807 (4)22/295 (7)†P < .05 versus controls.‡Standardized mean difference greater than 0.15 versus controls. Mild psoriasis was defined as PASI below five in the absence of phototherapy and systemics, and moderate-to-severe psoriasis was defined as PASI above five or treatment with phototherapy and systemics.7/145 (5) Hepatitis13/806 (2)5/297 (2)2/147 (1) Inflammatory bowel disease12/809 (1)3/298 (1)3/147 (2)IQR, Interquartile range; SD, standard deviation.∗ With the exception of age at indexation, all characteristics were measured at enrolment.† P < .05 versus controls.‡ Standardized mean difference greater than 0.15 versus controls. Mild psoriasis was defined as PASI below five in the absence of phototherapy and systemics, and moderate-to-severe psoriasis was defined as PASI above five or treatment with phototherapy and systemics.§ P < .001 versus controls. Open table in a new tab IQR, Interquartile range; SD, standard deviation. The cumulative incidence of respiratory infection is presented in Fig 1. Follow-up and incidence are presented Supplementary Table 4 (Table S3.1; available at https://data.mendeley.com/datasets/vh2k3nvsn9/1). In multivariable analyses psoriasis was associated with increased risk of inpatient or specialist outpatient diagnosed respiratory infection: hazard ratios of 2.0 (95%confidence interval [CI], 1.1-3.6) for patients with mild disease; and 2.5 (95% CI, 1.3-4.9) for patients with moderate-to-severe disease. In multivariable analysis of prescriptions, mild disease was associated with an incidence rate ratio of 1.3 (95% CI, 1.1-1.5) and moderate-to-severe disease with an incidence rate ratio of 1.5 (95% CI, 1.2-1.9). The 121 patients treated with immunosuppressants were on average exposed to immunosuppressants for 3.1 years and unexposed to immunosuppressants for 5.4 years. The incidence of infection per person-year on and off immunosuppressive treatment was estimated at 0.31 and 0.29, respectively (P = .31). Psoriasis is associated with increased risk of respiratory infection independently of known risk factors for infection, with moderate-to-severe psoriasis conferring higher risk than mild psoriasis. Immunosuppressive treatment did not further increase the risk for respiratory infection. These findings can inform risk mitigation strategies and preventive efforts for patients with psoriasis during the COVID-19 pandemic. Limitations include data on infections not coming to clinical attention and generalizability. Axel Svedbom is an employee of ICON plc, a contract research organization. Lotus Mallbris is an employee of Eli Lilly and Company. Mona Ståhle has received honoraria for serving as an advisor and for participating in symposia arranged by Abbvie, Novartis, Pfizer, Eli Lilly, Janssen-Cilag, and Leo Pharma.