High seroprevalence for typhus group rickettsiae, southwestern Tanzania

Rickettsioses caused by typhus group rickettsiae have been reported in various African regions. We conducted a cross-sectional survey of 1,227 participants from 9 different sites in the Mbeya region, Tanzania; overall seroprevalence of typhus group rickettsiae was 9.3%. Risk factors identified in multivariable analysis included low vegetation density and highway proximity.

Low specificity of determine HIV1/2 RDT using whole blood in south west Tanzania

Objective

To evaluate the diagnostic performance of two rapid detection tests (RDTs) for HIV 1/2 in plasma and in whole blood samples.

Methods

More than 15,000 study subjects above the age of two years participated in two rounds of a cohort study to determine the prevalence of HIV. HIV testing was performed using the Determine HIV 1/2 test (Abbott) in the first (2006/2007) and the HIV 1/2 STAT-PAK Dipstick Assay (Chembio) in the second round (2007/2008) of the survey. Positive results were classified into faint and strong bands depending on the visual appearance of the test strip and confirmed by ELISA and Western blot.

Results

The sensitivity and specificity of the Determine RDT were 100% (95% confidence interval  = 86.8 to 100%) and 96.8% (95.9 to 97.6%) in whole blood and 100% (99.7 to 100%) and 97.9% (97.6 to 98.1%) in plasma respectively. Specificity was highly dependent on the tested sample type: when using whole blood, 67.1% of positive results were false positive, as opposed to 17.4% in plasma. Test strips with only faint positive bands were more often false positive than strips showing strong bands and were more common in whole blood than in plasma. Evaluation of the STAT-PAK RDT in plasma during the second year resulted in a sensitivity of 99.7% (99.1 to 99.9%) and a specificity of 99.3% (99.1 to 99.4%) with 6.9% of the positive results being false.

Conclusions

Our study shows that the Determine HIV 1/2 strip test with its high sensitivity is an excellent tool to screen for HIV infection, but that – at least in our setting – it can not be recommended as a confirmatory test in VCT campaigns where whole blood is used.

High seroprevalence of Rift Valley FEVER AND EVIDENCE FOR ENDEMIC circulation in Mbeya region, Tanzania, in a cross-sectional study

Background

The Rift Valley fever virus (RVFV) is an arthropod-borne phlebovirus. RVFV mostly causes outbreaks among domestic ruminants with a major economic impact. Human infections are associated with these events, with a fatality rate of 0.5–2%. Since the virus is able to use many mosquito species of temperate climates as vectors, it has a high potential to spread to outside Africa.

Methodology/Principal Findings

We conducted a stratified, cross-sectional sero-prevalence survey in 1228 participants from Mbeya region, southwestern Tanzania. Samples were selected from 17,872 persons who took part in a cohort study in 2007 and 2008. RVFV IgG status was determined by indirect immunofluorescence. Possible risk factors were analyzed using uni- and multi-variable Poisson regression models. We found a unique local maximum of RVFV IgG prevalence of 29.3% in a study site close to Lake Malawi (N = 150). The overall seroprevalence was 5.2%. Seropositivity was significantly associated with higher age, lower socio-economic status, ownership of cattle and decreased with distance to Lake Malawi. A high vegetation density, higher minimum and lower maximum temperatures were found to be associated with RVFV IgG positivity. Altitude of residence, especially on a small scale in the high-prevalence area was strongly correlated (PR 0.87 per meter, 95% CI = 0.80–0.94). Abundant surface water collections are present in the lower areas of the high-prevalence site. RVF has not been diagnosed clinically, nor an outbreak detected in the high-prevalence area.

Conclusions

RVFV is probably circulating endemically in the region. The presence of cattle, dense vegetation and temperate conditions favour mosquito propagation and virus replication in the vector and seem to play major roles in virus transmission and circulation. The environmental risk-factors that we identified could serve to more exactly determine areas at risk for RVFV endemicity.

We describe a high seropositivity rate for Rift Valley fever virus, in up to 29.3% of tested individuals from the shore of Lake Malawi in southwestern Tanzania, and much lower rates from areas distant to the lake. Rift Valley fever disease or outbreaks have not been observed there in the past, which suggests that the virus is circulating under locally favorable conditions and is either a non-pathogenic strain, or that occasional occurrence of disease is missed. We were able to identify a low socio-economic status and cattle ownership as possible socio-economic risk factors for an individual to be seropositive. Environmental risk factors associated with seropositivity include dense vegetation, and ambient land surface temperatures which may be important for breeding success of the mosquitoes which transmit Rift Valley fever, and for efficient multiplication of the virus in the mosquito. Low elevation of the home, and proximity to Lake Malawi probably lead to abundant surface water collections, which serve as breeding places for mosquitoes. These findings will inform patient care in the areas close to Lake Malawi, and may help to design models which predict low-level virus circulation.

Evaluation of Diagnos TB AG, a flow-through immunoassay for rapid detection of pulmonary tuberculosis

We evaluated the diagnostic performance of the Diagnos TB AG immunoassay in 171 Tanzanians with suspected pulmonary tuberculosis (TB). The sensitivity and specificity, and positive and negative predictive values of the rapid test for the detection of pulmonary TB in this population were respectively 60.0%, 33.3%, 40.3% and 52.6%. In its current configuration, this test will not help overcome difficulties in the rapid diagnosis of TB.

Stroke mortality in urban and rural Tanzania. Adult Morbidity and Mortality Project

BACKGROUND

Most data for stroke mortality in sub-Saharan Africa are hospital based. We aimed to establish the contribution of cerebrovascular disease to all-cause mortality and cerebrovascular disease mortality rates in adults aged 15 years or more in one urban and two rural areas of Tanzania.

METHODS

Regular censuses of the three surveillance populations consisting of 307,820 people (125,932 aged below 15 years and 181,888 aged 15 or more) were undertaken with prospective monitoring of all deaths arising in these populations between June 1, 1992 and May 31, 1995. Verbal autopsies were completed with relatives or carers of the deceased to assess, when possible, the cause of death.

FINDINGS

During the 3-year observation period 11,975 deaths were recorded in the three surveillance areas, of which 7629 (64%) were in adults aged 15 years or more (4088 [54%] of these in men and 3541 [46%] in women). In the adults, 421 (5.5%) of the deaths were attributed to cerebrovascular disease, 225 (53%) of these in men and 196 (47%) in women. The yearly age-adjusted rates per 100,000 in the 15-64 year age group for the three project areas (urban, fairly prosperous rural, and poor rural, respectively) were 65 (95% CI 39-90), 44 (31-56), and 35 (22-48) for men, and 88 (48-128), 33 (22-43), and 27 (16-38) for women, as compared with the England and Wales (1993) rates of 10.8 (10.0-11.6) for men and 8.6 (7.9-9.3) for women.

INTERPRETATION

We postulate that the high rates in Tanzania were due to untreated hypertension. Our study assessed mortality over a single time period and therefore it is not possible to comment on trends with time. However, ageing of the population is likely to lead to a very large increase in mortality from stroke in the future.

Application of the new ADA criteria for the diagnosis of diabetes to population studies in sub-Saharan Africa. American diabetes association

AIMS

To examine the implications for epidemiological studies of the American Diabetes Association (ADA) recommendation that the fasting blood glucose at a lowered level becomes the main diagnostic test for diabetes on cross-sectional-based data from sub-Saharan Africa.

METHODS

Data from 11 surveys conducted in rural, peri-urban and urban Cameroon (n = 1804), South Africa (n = 3799) and Tanzania (n = 10013) which measured fasting (ADA criteria) and 2-h blood glucose concentrations during a standard 75 g OGTT (old WHO criteria) were analysed.

RESULTS

The prevalence of diabetes was higher in eight of the 11 surveys when applying the new ADA compared to the old WHO criteria. With the exception of one population (Mara, Tanzania) the absolute difference in prevalence between the two classifications tended to be small (< 2%). There was considerable variation in the categorization of individuals using the ADA and old WHO criteria. The level of agreement between the two ranged from fair to good (Kappa statistic 0.17-0.86). The prevalence of impaired fasting glycaemia (IFG) was lower than that of impaired glucose tolerance (IGT) in 10 of the surveys and the agreement between the two was fair, < or = 0.26 in all the surveys.

CONCLUSIONS

Although the use of the new ADA fasting criteria for prevalence surveys is an attractive and practical option, particularly in Africa, further information is required on the characteristics and prognosis of individuals classified as IFG or diabetic by the fasting criteria, prior to wide adoption of the ADA criteria. Ideally measurement of both fasting and two low glucose concentrations should remain the standard for epidemiological studies.

The use of morbidity questionnaires to identify communities with high prevalences of schistosome or geohelminth infections in Tanzania

Parasitic infections were investigated in Morogoro Rural District, Tanzania, between October 1992 and June 1993. A total of 4589 schoolchildren (aged 7-17 years) from 30 primary schools was screened for infection with Ascaris lumbricoides, Trichuris trichiura, hookworms (3456 children only), Schistosoma mansoni and S. haematobium. The children were also asked about their recent experiences of the following: diarrhoea, abdominal pain, blood in stool, perception of suffering from schistosomiasis, and worm infection and examined for spleen and liver enlargement. Among schools, there were correlations between the prevalence of S. mansoni infection and bloody stools, spleen enlargement and liver enlargement, and between S. haematobium infection and the presence of blood in urine. To exclude ecological explanations for the correlations, logistic regression was used to estimate the adjusted odds ratio (OR) for each infection and each sign or symptom. No sign or symptom was significantly associated with any geohelminth infection. Reported blood in stool was significantly associated with S. mansoni infection (OR = 1.62, P = 0.045). Reported blood in urine was significantly associated with S. haematobium infection (OR = 7.71, P < 0.001), as was reported blood in stool (OR = 11.52, P < 0.001), indicating that presence of blood in either form of excreta was related to the local term for schistosomiasis. These results support the possibility of using reported blood in stool as a means of rapid assessment for identifying communities with a high prevalence of S. mansoni infection.

Outlook for survivors of childhood in sub-Saharan Africa: adult mortality in Tanzania. Adult Morbidity and Mortality Project

OBJECTIVE

To measure age and sex specific mortality in adults (15-59 years) in one urban and two rural areas of Tanzania.

DESIGN

Reporting of all deaths occurring between 1 June 1992 and 31 May 1995.

SETTING

Eight branches in Dar es Salaam (Tanzania's largest city), 59 villages in Morogoro rural district (a poor rural area), and 47 villages in Hai district (a more prosperous rural area).

SUBJECTS

40,304 adults in Dar es Salaam, 69,964 in Hai, 50,465 in Morogoro rural.

MAIN OUTCOME MEASURES

Mortality and probability of death between 15 and 59 years of age (45Q15).

RESULTS

During the three year observation period a total of 4929 deaths were recorded in adults aged 15-59 years in all areas. Crude mortalities ranged from 6.1/1000/year for women in Hai to 15.9/1000/year for men in Morogoro rural. Age specific mortalities were up to 43 times higher than rates in England and Wales. Rates were higher in men at all ages in the two rural areas except in the age group 25 to 29 years in Hai and 20 to 34 years in Morogoro rural. In Dar es Salaam rates in men were higher only in the 40 to 59 year age group. The probability of death before age 60 of a 15 year old man (45Q15) was 47% in Dar es Salaam, 37% in Hai, and 58% in Morogoro; for women these figures were 45%, 26%, and 48%, respectively. (The average 45Q15s for men and women in established market economies are 15% and 7%, respectively.)

CONCLUSION

Survivors of childhood in Tanzania continue to show high rates of mortality throughout adult life. As the health of adults is essential for the wellbeing of young and old there is an urgent need to develop policies that deal with the causes of adult mortality.