Myopia in secondary school students in Mwanza City, Tanzania: the need for a national screening programme

BACKGROUND/AIMS

The prevalence of significant refractive errors and other eye diseases was measured in 2511 secondary school students aged 11-27 years in Mwanza City, Tanzania. Risk factors for myopia were explored.

METHODS

A questionnaire assessed the students' socioeconomic background and exposure to near work followed by visual acuity assessment and a full eye examination. Non-cycloplegic objective and subjective refraction was done on all participants with visual acuity of worse than 6/12 in either eye without an obvious cause.

RESULTS

154 (6.1%) students had significant refractive errors. Myopia was the leading refractive error (5.6%). Amblyopia (0.4%), strabismus (0.2%), and other treatable eye disorders were uncommon. Only 30.3% of students with significant refractive errors wore spectacles before the survey. Age, sex, ethnicity, father's educational status, and a family history of siblings with spectacles were significant independent risk factors for myopia.

CONCLUSION

The prevalence of uncorrected significant refractive errors is high enough to justify a regular school eye screening programme in secondary schools in Tanzania. Risk factors for myopia are similar to those reported in European, North-American, and Asian populations.

Predicting the distribution of urinary schistosomiasis in Tanzania using satellite sensor data

In this paper, remotely sensed (RS) satellite sensor environmental data, using logistic regression, are used to develop prediction maps of the probability of having infection prevalence exceeding 50%, and warranting mass treatment according to World Health Organization (WHO) guidelines. The model was developed using data from one area of coastal Tanzania and validated with independent data from different areas of the country. Receiver operating characteristic (ROC) analysis was used to evaluate the model's predictive performance. The model allows reasonable discrimination between high and low prevalence schools, at least within those geographical areas in which they were originally developed, and performs reasonably well in other coastal areas, but performs poorly by comparison in the Great Lakes area of Tanzania. These results may be explained by reference to an ecological zone map based on RS-derived environmental data. This map suggests that areas where the model reliably predicts a high prevalence of schistosomiasis fall within the same ecological zone, which has common intermediate-host snail species responsible for transmission. By contrast, the model's performance is poor near Lake Victoria, which is in a different ecological zone with different snail species. The ecological map can potentially define a template for those areas where existing models can be applied, and highlight areas where further data and models are required. The developed model was then used to provide estimates of the number of schoolchildren at risk of high prevalence and associated programme costs.

Predictors of HIV-1 serostatus disclosure: a prospective study among HIV-infected pregnant women in Dar es Salaam, Tanzania

OBJECTIVES

To examine the socio-demographic and behavioral factors predictive of women's disclosure of an HIV-positive test result in Dar es Salaam, Tanzania.

DESIGN

From April 1995 to May 2000, 1078 HIV-positive pregnant women participated in an ongoing randomized trial on micronutrients and HIV-1 vertical transmission and progression. Disclosure to a partner or to a female relative was assessed 2 months after post-test counseling and at 6 monthly follow-up visits. Socio-demographic, health, behavioral and psychological factors were measured at baseline and during follow-up.

METHODS

Predictors of time to disclosure of HIV serostatus were determined using Cox proportional hazards regression models.

RESULTS

Prevalence of disclosure to a partner ranged from 22% within 2 months to 40% after nearly 4 years. Women were less likely to disclose to their partners if they were cohabiting, had low wage employment, had previously disclosed to a female relative, or reported ever-use of a modern contraceptive method. Women reporting fewer than six lifetime sexual partners or knowing someone with HIV/AIDS were more likely to disclose to their partners. Disclosure to a female relative was predicted by knowing more than two individuals with HIV/AIDS, full economic dependency on their partner, high levels of social support, and prior attendance at a support group meeting.

CONCLUSIONS

A substantial proportion of HIV-infected pregnant women never disclosed their result to a partner or a close female relative. Lack of disclosure may have limited their ability to engage in preventive behaviors or to obtain the necessary emotional support for coping with their serostatus or illness.

The availability of potential hosts as a determinant of feeding behaviours and malaria transmission by African mosquito populations

A simple model for the influence of host availability on vector bloodmeal choice is applied to estimate the relative availabilities of humans, cattle and other host populations to malaria vectors in African communities, using published human blood indices and ratios of cattle to humans. Cattle were bitten < 0.01, 0.021 +/- 0.11, 1.61 +/- 0.16 and 1.61 +/- 0.46 times as often as humans by Anopheles funestus, An. gambiae sensu stricto and An. arabiensis in Segera, Tanzania, and An. gambiae sensu lato in The Gambia, respectively. No significant feeding upon host species other than cattle or humans was detected. Even though An. gambiae s.l. in The Gambia were mostly An. gambiae s.s., they were 77 times more likely to choose cattle over humans than An. gambiae s.s. in Tanzania. The model accurately predicted cattle blood indices for the An. arabiensis population in Tanzania (predicted = 0.99 +/- 0.21 x observed + 0.00 +/- 0.10; r2 = 0.66). The potential effect of increased cattle abundance upon malaria transmission intensity was simulated using fitted relative availability parameters and assuming vector emergence rate, feeding cycle length and survivorship were unaffected. The model predicted that increased cattle populations would not affect malaria transmission in Tanzania but could drastically reduce transmission in The Gambia or where An. arabiensis is the dominant vector. We define the availability of a host as the rate at which a typical individual host-seeking vector encounters and feeds upon that host in a single feeding cycle. Mathematical models based on this definition also represent promising tools for quantifying the dependence of vector longevity, feeding cycle length and dispersal upon host availability.