The remaining incidence studies were conducted in Caribbean countries not plainly representative of developing countries. The level of socioeconomic development in the three Caribbean countries is relatively high for the developing world.

Based on the United Nations Development Programme (1998), Barbados ranked 2nd,  Trinidad 13th,  and Jamaica 45th highest among developing nations.  The health indicators and standards of living for these countries may be considered intermediate on the development continuum.

The three Caribbean studies (Hickling and Rodgers-Johnson, 1995; Bhugra et al., 1996; Mahy et al., 1999) emulated the design used in the WHO Ten Country Study: all patients making first contact with care agencies for a possible schizophrenic episode during a 1-year period were assessed for schizophrenia. The rates per 10000 person-years at risk for narrowly defined schizophrenia (CATEGO S+) were 2.1 (Jamaica), 1.6 (Trinidad) and 2.8 (Barbados).

For schizophrenia using a broad CATEGO definition,  the rates per 10000 were 2.4 (SPO schizophrenia, Jamaica),  2.2 (SPO+  schizophrenia,Trinidad)  and 3.2 (SPO+  schizophrenia, Barbados). It should be noted that the rates for the narrow and broad diagnoses are quite similar, as there were few non-S+ cases reported by these sites. Relative to findings in the Ten Country Study, the point estimates for CATEGO S+ incidence rates in the Caribbean countries (range 1.6 - 2.8 per 10000) were higher than those reported at any Ten Country Study site (range 0.7 - 1.4 per 10000). For schizophrenia broadly defined using equivalent diagnostic classifications (SPO, SPO+) the Caribbean rates are higher than those reported by the WHO study developed country sites, except Moscow, and similar to those reported by developing country sites.

What does the total evidence suggest about variation in incidence of schizophrenia between developing and developed countries? Clearly there are insuficient data to support the claim that there is no difference in incidence between these two settings.

However, the existing evidence is also insuficient for any inference of systematic variation across developing and developed countries. In sum, a strong case can be made for variation in incidence across place, but a patterned distribution based on country level of development is inconclusive.

Nonaffective acute remitting psychosis

It would be wrong, however, to conclude that no evidence has emerged from incidence studies relating to systematic variation in any nonaffective psychoses between developing and developed countries. Susser and collaborators found evidence for a distinct nonaffective psychotic disorder that mainly occurs in the developing world.  Susser and Wanderling (1994)  reported a marked variation in incidence of nonaffective acute remitting psychosis (NARP)  between developed and developing country settings. The incidence of NARP was 10-fold greater in the developing than developed country settings in the Ten Country Study.

Susser and colleagues have argued that such results support the idea of a distinct disorder. Biological as well as cultural influences are suspected in the aetiology of these psychotic disorders (Collins et al., 1996, 1999). In one study, patients with NARP were more likely to have experienced fever in the 12 weeks preceding onset than controls (odds ratio 6.2).

Moreover,  this class of remitting psychotic disorders constitutes a potential source of misclassified cases in studies of schizophrenia. In fact, all patients with NARP that Susser and Wanderling (1994) identified had been diagnosed, by their definition of NARP, with ICD-9 schizophrenia. The influence of NARP on incidence rates of schizophrenia,  however,  does not explain most of the difference between developed and developing countries in the incidence of schizophrenia broadly defined in the Ten Country Study, or the differential in incidence suspected based on the preliminary data on ICD-10 schizophrenia.  Differences remained after removing those with NARP.

Some other differences between developing and developed countries remain unexplained. In particular, differences in the frequencies of psychotic individuals diagnosed as catatonic in the Ten Country Study (10% in developing countries and extremely rare in developed countries) have not been accounted for. Together with the finding of high rates of NARP in developing country settings, the evidence suggests possible aetiologic and disease diversity across the developing/developed
divide.

Michaeline Bresnahan, Paulo Menezes, Vijoy Varma and Ezra Susser
Division of Epidemiology, Columbia University, New York, USA
Department of Preventative Medicine, University of Sao Paulo, Brazil

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