Determinants of Cluster Size in Large, Population-Based Molecular Epidemiology Study of Tuberculosis, Northern Malawi

Both epidemiologic and strain-related factors may contribute to large clusters of tuberculosis patients

Profile: the Karonga Health and Demographic Surveillance System

The Karonga Health and Demographic Surveillance System (Karonga HDSS) in northern Malawi currently has a population of more than 35 000 individuals under continuous demographic surveillance since completion of a baseline census (2002–2004). The surveillance system collects data on vital events and migration for individuals and for households. It also provides data on cause-specific mortality obtained by verbal autopsy for all age groups, and estimates rates of disease for specific presentations via linkage to clinical facility data. The Karonga HDSS provides a structure for surveys of socio-economic status, HIV sero-prevalence and incidence, sexual behaviour, fertility intentions and a sampling frame for other studies, as well as evaluating the impact of interventions, such as antiretroviral therapy and vaccination programmes. Uniquely, it relies on a network of village informants to report vital events and household moves, and furthermore is linked to an archive of biological samples and data from population surveys and other studies dating back three decades

Mycobacterium tuberculosis Beijing Genotype, Northern Malawi

In a 7-year population-based study in Malawi, we showed that Beijing genotype tuberculosis (TB) increased as a proportion of TB cases. All the Beijing genotype strains were fully drug sensitive. Contact histories, TB type, and case-fatality rates were similar for Beijing and non-Beijing genotype TB

Tuberculosis Transmission Attributable to Close Contacts and HIV Status, Malawi

In this population, ≈90% of M. tuberculosis infections were transmitted by casual contact, and nearly half from HIV-positive patients

Estimating the global conservation status of more than 15,000 Amazonian tree species

Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict thatmost of the world’s >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century

Polio control after certification: major issues outstanding

Now that the global eradication of wild poliovirus is almost within sight, planning for the post-certification era is becoming a priority issue. It is agreed that a stockpile of appropriate polio vaccines will need to be established, and a surveillance and response capacity will need to be maintained, in order to protect the world against any possible future outbreaks attributable either to the persistence of wild poliovirus or vaccine-derived polioviruses (VDPVs) or to the unintentional or intentional release of poliovirus from a laboratory or vaccine store. Although it has been suggested that the stockpile should consist of monovalent oral poliovirus vaccine (mOPV), many questions remain concerning its nature, financing, management, and use - in particular, because of uncertainties over future national vaccination policies, and over the availability of different vaccines, after the certification of wild poliovirus eradication. There are further uncertainties concerning the possible role and efficacy of inactivated poliovirus vaccine (IPV) used either routinely or in outbreak control in low-hygiene settings, the potential for rapid geographical spread of polioviruses should an outbreak occur after certification, and the risks inherent in introducing additional oral polio vaccine (OPV) viruses into populations in which the vaccine coverage and prevalence of immunity have declined, and which may thus favour the spread of VDPVs. Given these important gaps in knowledge, no country should discontinue polio vaccination until a coordinated policy for the post-certification era has been developed and the recommended measures have been put in place

Annual Mycobacterium tuberculosis infection risk and interpretation of clustering statistics.

Several recent studies have used proportions of tuberculosis cases sharing identical DNA fingerprint patterns (i.e., isolate clustering) to estimate the extent of disease attributable to recent transmission. Using a model of introduction and transmission of strains with different DNA fingerprint patterns, we show that the properties and interpretation of clustering statistics may differ substantially between settings. For some unindustrialized countries, where the annual risk for infection has changed little over time, 70% to 80% of all age groups may be clustered during a 3-year period, which underestimates the proportion of disease attributable to recent transmission. In contrast, for a typical industrialized setting (the Netherlands), clustering declines with increasing age (from 75% to 15% among young and old patients, respectively) and underestimates the extent of recent transmission only for young patients. We conclude that, in some settings, clustering is an unreliable indicator of the extent of recent transmission

Cotrimoxazole prophylaxis reduces mortality in human immunodeficiency virus-positive tuberculosis patients in Karonga District, Malawi

OBJECTIVE: To estimate the impact of cotrimoxazole prophylaxis on the survival of human immunodeficiency virus (HIV)-positive tuberculosis (TB) patients. METHODS: A cohort study with a historical comparison group was conducted. End-of-treatment outcomes and 18-month survival were compared between TB patients registered in 1999 and patients registered in 2000 in Karonga District, Malawi. Case ascertainment, treatment and outpatient follow-up were identical in the two years except that in 2000 cotrimoxazole prophylaxis was offered to HIV-positive patients in addition to routine care. The prophylaxis was provided from the time a patient was identified as HIV-positive until 12 months after registration. Analyses were carried out on an intention-to-treat basis for all TB patients, and also separately by HIV status, TB type and certainty of diagnosis. FINDINGS: 355 and 362 TB patients were registered in 1999 and 2000, respectively; 70% were HIV-positive. The overall case fatality rate fell from 37% to 29%, i.e. for every 12.5 TB patients treated, one death was averted. Case fatality rates were unchanged between the two years in HIV-negative patients, but fell in HIV-positive patients from 43% to 24%. The improved survival became apparent after the first 2 months and was maintained beyond the end of treatment. The improvement was most marked in patients with smear-positive TB and others with confirmed TB diagnoses. CONCLUSION: Survival of HIV-positive TB patients improved dramatically with the addition of cotrimoxazole prophylaxis to the treatment regimen. The improvement can be attributed to cotrimoxazole because other factors were unchanged and the survival of HIV-negative patients was not improved. Cotrimoxazole prophylaxis should therefore be added to the routine care of HIV-positive TB patients