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Comorbidity of schizophrenia and infection: a population-based cohort study
Philip Rising Nielsen1,2, Thomas Munk Laursen3,4, Esben Agerbo3,4,5
1National Centre for Register-based Research, Aarhus University, Fuglesangs Allé 4, 8210, Aarhus V, Denmark. prn@econ.au.dk.
Purpose:
In this paper, we investigate the hypothesis that there is an overlap between infection and schizophrenia. Infections have been identified as a risk factor for schizophrenia, but the possible overlap between schizophrenia and infections remains unidentified so far. Here, we describe the use of the comorbidity index, a method for objectively integrating associations into a single measure estimating overlap.
Methods:
Data were drawn from three population-based registers, the Civil Registration Register, the Danish Psychiatric Central Research Register, and the Danish National Hospital Register. We selected a cohort of 1,403,183 persons born in Denmark 1977-2002.
Results:
Our results indicate that persons who have had a hospital contact with an infection (IRR 1.53, CI 1.46-1.61) are more likely to develop schizophrenia than persons who have not had such a contact. Persons who have had a diagnosis with schizophrenia are more likely to have had a hospital contact with an infection (IRR 1.73, 95 % CI 1.57-1.91) than persons who have had no schizophrenia diagnosis. A comorbidity index of 1.40 (95 % CI 1.34-1.46) was found, indicating an overlap between schizophrenia and infection.
Conclusion:
Our findings indicate that schizophrenia and infections overlap and that they share risk factors. The comorbidity index showed that the co-occurrence of schizophrenia and infection was 40 % higher than if the two disorders had occurred independently. Although the incidence of schizophrenia and infection was associated with each factor, the overlap could not be explained by urbanicity, parental history of psychiatric admission and infection.
Insights
Infections are a significant risk factor for schizophrenia, with a 40% higher co-occurrence than expected. This study quantifies the overlap between infection and schizophrenia, suggesting shared risk factors.
Area of Science:
- Psychiatry
- Infectious Diseases
- Epidemiology
Background:
- Infections are recognized as a potential risk factor for schizophrenia.
- The precise overlap and shared risk factors between infection and schizophrenia remain largely unidentified.
- Objective quantification of this relationship is needed.
Purpose of the Study:
- To investigate the hypothesis of an overlap between infection and schizophrenia.
- To objectively measure the association between infection and schizophrenia using a comorbidity index.
- To explore shared risk factors contributing to the co-occurrence of these conditions.
Main Methods:
- Utilized data from three Danish population-based registers: Civil Registration Register, Danish Psychiatric Central Research Register, and Danish National Hospital Register.
- A cohort of 1,403,183 individuals born between 1977 and 2002 in Denmark was analyzed.
- A comorbidity index was employed to quantify the overlap between infection and schizophrenia.
Main Results:
- Individuals with a hospital contact for infection showed a 1.53 times higher likelihood of developing schizophrenia (IRR 1.53, CI 1.46-1.61).
- Patients diagnosed with schizophrenia had a 1.73 times higher likelihood of prior hospital contact for infection (IRR 1.73, 95% CI 1.57-1.91).
- A comorbidity index of 1.40 (95% CI 1.34-1.46) indicated a significant overlap, suggesting a 40% higher co-occurrence than independent occurrence.
Conclusions:
- Schizophrenia and infections demonstrate a significant overlap, indicating shared underlying risk factors.
- The observed co-occurrence is 40% higher than would be expected if the conditions occurred independently.
- This overlap could not be attributed to factors such as urbanicity or parental history of psychiatric admission or infection.
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