From the Editor

A few years ago, Czech scientist Jaroslav Flegr made a splash by arguing that our feline friends were causing psychosis in people – The Atlantic provocatively titled their article on him: “How Your Cat is Making You Sick.” Flegr’s argument was based in part on several papers (including by prominent researcher E. Fuller Torrey) noting that cat ownership confers an increased risk of psychotic disorders like schizophrenia.

So, are cats safe for household use?

In our first selection, we look at a new Psychological Medicine paper that, with a cohort study, finds no connection between cat ownership and psychotic symptoms.

Good news, tabby: you can stay

How to help the homeless? In our second selection, drawing from The Guardian, we look at a Hawaiian effort to prescribe the housing to the homeless – literally.

Please note that there will be no Readings for the next two weeks. Enjoy the March break.


Pets and Problems

“Curiosity killed the cat: no evidence of an association between cat ownership and psychotic symptoms at ages 13 and 18 years in a UK general population cohort”

F. Solmi, J. F. Hayes, G. Lewis, J. B. Kirkbride

Psychological Medicine, 22 February 2017 Online


House cats are the primary hosts of Toxoplasma gondii, a protozoan parasite that can infect various warm-blooded animals, including humans. Infection can occur in utero or postnatally, via ingestion of either the parasite’s oocysts–which might be present in soil, water, or food–or tissue cysts from infected animals (e.g. in raw or undercooked meat). In intermediate hosts (e.g. humans or animals other than cats), the parasite exploits lymphocytes to encroach in muscle tissues and, importantly, the brain, where it can form tissue cysts in neurons, microglia, and astrocytes.

Although the evidence is not unequivocal, data from several epidemiological, experimental, and animal studies suggests that T. gondii infection may be implicated in the aetiology of psychosis. For example, dopaminergic dysfunction and cognitive impairments – similar to those observed in people with schizophrenia–have been observed in infected rodents and humans; these people may also experience hallucinations during acute infection with the parasite. A recent meta-analysis of 38 studies found that compared with controls, people with schizophrenia were nearly three times more likely to be seropositive for T. gondii antibodies [odds ratio (OR) 2.71, 95% confidence interval (CI) 1.93– 3.80]. Higher seroprevalence and serointensity of T. gondii IgG (but not IgM, an indicator of recent infection) in people with schizophrenia and their mothers suggest that either early life exposure to the parasite, congenital infection, or transmission of maternal antibodies could alter neuro-development of subsequent offspring.

Assuming a causal relationship between T. gondii infection and later psychosis, some researchers have hypothesized that cat ownership should confer an increased risk of psychotic disorders…

Francesca Solmi

So begins a paper by Solmi et al. that seeks to test this hypothesis by looking at cat ownership in pregnancy and childhood, and whether ownership is associated with psychotic experiences (PEs) in early and late adolescence.

Here’s what they did.

· The authors drew data from the Avon Longitudinal Study of Parents and Children (ALSPCA) study, which had “invited 16734 pregnant women expected to deliver between 1 April 1991 and 31 April 1992 resident in the former county of Avon (England) to participate.”

· Information on pet ownership was reported “by mothers via postal questionnaires during pregnancy, and subsequently when their child was aged 8, 21, 31 and 47 months.”

· “At approximately ages 13 and 18 years, children attended clinic visits where they were administered the psychotic-like symptoms interview (PLIKSi), a semi-structured interviewer-rated screening assessment for PEs [psychotic experiences].”

· Statistical analysis was done. The authors used logical regression to consider if cat ownership had an association with psychotic experiences, and adjusted for socioeconomic factors (like overcrowding).

Here’s what they found:

· The sample: 6,705 at age 13 and 4,676 at age 18 had complete data on psychotic symptoms. Of those, 776 (11.57%) and 370 (7.91%) had psychotic symptoms that were suspected or definite at 13 and 18 years, respectively.

· Demographically: The youth included in the study included slightly more female than male (51.03% at age 13), were overwhelmingly white (96.05%), and had a mother who has married (81.24%).

· “Cat ownership in pregnancy was not associated with psychotic symptoms at age 13 or 18 years in either univariable (age 13: OR 1.15; age 18; OR 1.08) or in multivariable (age 13: adjusted OR 1.15; age 18; OR 1.08) models…”

· “Owning a cat at age 4 years was associated with higher odds of having PEs at age 13 years in univariable models (OR 1.23), but this effect was no longer significant after multivariable adjustment (OR 1.18).

· “There was no evidence that cat ownership at age 4 years was associated with PEs at age 18 years (univariable OR 1.11; adjusted OR 0.97).”

In sum:

We found no evidence that cat ownership in pregnancy or childhood was associated with PEs in early and late adolescence using prospectively collected data from a large population-based cohort, following control for several confounders and methods that investigate the likely impact of missing data.

A few thoughts:

1. This is a good study.

2. The research question is topical and catchy. This paper was picked up widely, including CNN.

3. On the results, lead authorFrancesca Solmi commented: “The message for cat owners is clear: there is no evidence that cats pose a risk to children’s mental health…” But why do these results differ so greatly from the earlier literature? This paper had a significantly different methodology – among other things: they did a cohort study with data stretching for years; in the statistical analysis, the authors also sought to rule out other factors.

4. The authors did weigh this, and argue for the strength of their approach. They also question earlier studies: “Previous reports of positive associations between cat ownership and schizophrenia may therefore have been attributable to Type I error, particularly given the small sample sizes and lack of control for confounders inherent to some studies.” But by attempting to statistically eliminate confounders, did they end up compromising the data? In a CNN interview, researcher E. Fuller Torrey – who was the lead author on several papers on schizophrenia and cat ownership – suggested as much (specifically about overcrowding). The CNN article can be read here:

Housing and Homelessness

“Doctors could prescribe houses to the homeless under radical Hawaii bill”

Liz Barney

The Guardian, 28 February 2017 Online


One day last month, Stephen Williams asked a passerby for help and then collapsed on the sidewalk. When the ambulance arrived in downtown Honolulu, his temperature was well over 104F.

A life-threatening staph infection had entered his bloodstream. Williams, who lives on the dusty streets of Chinatown, spent seven days hooked to an IV, treatment that can cost $40,000, according to the hospital that admitted him. But Williams didn’t pay: the bill was covered by government dollars in the form of Medicaid. Over the past four years, he has been to the hospital for infections 21 times, he said, a consequence of psoriasis flare-ups in a humid climate and unsanitary conditions.

Cases such as these have prompted a groundbreaking new proposal in Hawaii. Instead of prescribing medication to homeless patients like Williams, what if doctors could prescribe something else that might ameliorate their health problems more effectively? The prescription would be housing.

Liz Barney

So begins a Guardian article by Liz Barney. The article describes the effort of State Senator Josh Green, who is a physician, to classify homelessness as a medical condition. People then could be “prescribed” housing.

The article notes the connection between homelessness and health costs.

· In a recent study by a Hawaiian insurer, a small percentage of Medicaid users account for over half of the $2 billion of annual spending; high needs users were often dealing with homelessness.

· Housing reduces health care costs for the homeless by 43%.

· Dr. Green notes that health spending on some homeless is $120,000 but housing would be just $18,000.

The article continues by noting supporters and critics of the approach. Kimo Carvalho of the Institute for Human Services notes the need for targeted funding, particularly in light of people “walking out” of housing.

A few thoughts:

1. The debate in Hawaii, like much of North America, has changed dramatically in recent years. A few years ago, Hawaii had strict laws on homelessness; today, Housing First is discussed. The Economist wrote about Hawaii and homelessness here:

2. Housing First is an active area of research. I’ll note the incredible work done in the area – and the Canadian connection. And, of course, we have looked at this in past Readings. See, for example:

3. What a great public-policy debate to watch unfold. #Progress


Reading of the Week. Every week I pick articles and papers from the world of Psychiatry.