Pablo Chaparro

High prevalence of sub-microscopic infections in Colombia

BackgroundMalaria transmission in Latin America is typically characterized as hypo-endemic and unstable with ~170 million inhabitants at risk of malaria infection. Although Colombia has witnessed an important decrease in malaria transmission, the disease remains a public health problem with an estimated ~10 million people currently living in areas with malaria risk and ~61,000 cases reported in 2012. This study aimed to establish the malaria prevalence in three endemic regions of Colombia to aid in designing new interventions for malaria elimination.MethodsA cross-sectional survey was conducted in three regions of Colombia with different malaria epidemiological profiles: Tierralta (Ta), Tumaco (Tu) and Buenaventura (Bv). The Annual Parasite Index (API) was 10.7, 6.9 and 3.1, respectively. Participants were asked to respond to a sociodemographic questionnaire and then were bled to determine the Duffy genotype and the prevalence of malaria infection by microscopy and quantitative real-time PCR (qPCR).ResultsThe study was conducted between October 2011 and January 2012. Eight sentinel sites with 1,169 subjects from 267 households were included. The overall prevalence of sub-microscopic infections measured by thick blood smear (TBS) was 0.3% (n = 4) whereas by qPCR it was 9.7% (n = 113), with a greater proportion (13%) in 40-50 years old individuals. Furthermore, different regions displayed different prevalence of sub-microscopic infections: Bv 12%, Ta 15%, and Tu 4%. From these 113 samples (qPCR), 74% were positive for P. vivax and 22% for P. falciparum, and 4% were mixed infections, which correlates to the overall parasite prevalence in Colombia. This study showed that in the southern Pacific coast of Colombia (Bv and Tu), around 56% of the population have a Duffy-negative genotype, compared to the northern region (Ta) where the percentage of Duffy-negative genotype is around 3%.ConclusionsSub-microscopic infections are prevalent across different regions in Colombia, particularly in areas with relatively low transmission intensity. The poor microscopy results suggest the need for more sensitive diagnostic tools for detection of sub-microscopic infections. This study underscores the importance of conducting active case surveillance to more accurately determine malaria incidence, and highlights the need for updating the malaria guidelines to track and treat sub-microscopic malaria infections.

Characterizing the malaria rural-to-urban transmission interface: The importance of reactive case detection

Background Reported urban malaria cases are increasing in Latin America, however, evidence of such trend remains insufficient. Here, we propose an integrated approach that allows characterizing malaria transmission at the rural-to-urban interface by combining epidemiological, entomological, and parasite genotyping methods. Methods/Principal findings A descriptive study that combines active (ACD), passive (PCD), and reactive (RCD) case detection was performed in urban and peri-urban neighborhoods of Quibdó, Colombia. Heads of households were interviewed and epidemiological surveys were conducted to assess malaria prevalence and identify potential risk factors. Sixteen primary cases, eight by ACD and eight by PCD were recruited for RCD. Using the RCD strategy, prevalence of 1% by microscopy (6/604) and 9% by quantitative polymerase chain reaction (qPCR) (52/604) were found. A total of 73 houses and 289 volunteers were screened leading to 41 secondary cases, all of them in peri-urban settings (14% prevalence). Most secondary cases were genetically distinct from primary cases indicating that there were independent occurrences. Plasmodium vivax was the predominant species (76.3%, 71/93), most of them being asymptomatic (46/71). Urban and peri-urban neighborhoods had significant sociodemographic differences. Twenty-four potential breeding sites were identified, all in peri-urban areas. The predominant vectors for 1,305 adults were Anopheles nuneztovari (56,2%) and An. Darlingi (42,5%). One An. nuneztovari specimen was confirmed naturally infected with P. falciparum by ELISA. Conclusions This study found no evidence supporting the existence of urban malaria transmission in Quibdó. RCD strategy was more efficient for identifying malaria cases than ACD alone in areas where malaria transmission is variable and unstable. Incorporating parasite genotyping allows discovering hidden patterns of malaria transmission that cannot be detected otherwise. We propose to use the term “focal case” for those primary cases that lead to discovery of secondary but genetically unrelated malaria cases indicating undetected malaria transmission.

[Characterization of the national malaria diagnostic network, Colombia, 2006-2010].

INTRODUCTION The implementation and development of activities of the quality assurance system of malaria diagnosis, allows the adequate operation of the national diagnostic network, needed to strengthen prevention and control actions of this important public health problem. OBJECTIVE To characterize the malaria diagnosis network in Colombia between 2006 and 2010. MATERIALS AND METHODS A retrospective study was made by reviewing the annual reports of malaria diagnosis network activities that were sent by the Public Health Laboratories (PHL) between 2006 and 2010. The study included analysis of diagnostic coverage in population at risk and an evaluation of activities and training to the people responsible for malaria diagnosis. RESULTS Malaria diagnostic coverage has increased in Colombia, from 53% of municipalities covered in 2006 to 80% in 2010. The number of places that perform diagnosis increased by 31% with a significant increase, for the same period, of the number of microscopists (56%) and laboratories (30%), to 1,195 and 1,780 respectively, registered in 2010. During the period of study, the percentage of PHL that carried out at least 3 of the activities of the quality assurance system for the diagnostic network at local level was 67%. CONCLUSIONS It is necessary to continue strengthening the malaria diagnosis network to provide timely and adequate diagnosis in order to reduce the morbidity and mortality by malaria.

Estimation of the underreporting of malaria measurement in ten municipalities of the Pacific coast of Nariño during 2009

INTRODUCTION The complete and effective collection of data of malaria cases is essential to formulate operative plans, as well as to develop and apply policies for its prevention and control. However, in Colombia, not all of the identified cases are notified nor incorporated into the surveillance system. This underreport represents a serious problem for decision makers. OBJECTIVE To estimate the type and quantity of errors made during the completion of the malaria individual case reporting form and its digitization level, through the use and monitoring of the reporting form in ten municipalities of Nariño in 2009. MATERIALS AND METHODS A descriptive cross-sectional study with a non-probabilistic and convenience sample of diagnosis and treatment sites was carried out. Copies of the reporting forms from these sites and of the Public Health Surveillance System database were taken to compare them case-by-case. Proportions were calculated. RESULTS In more than 60% of the 2,816 reporting forms of positive cases the information about municipality of residence, municipality of origin and occupation was not reported. The case-by-case comparison revealed that 845 (30.0%) notification forms were not digitized at all. Information of variables such as residence, name of the municipality, and date of onset of symptoms were neither complete nor exact in more than 50% of the cases. CONCLUSIONS The use of copies of the reporting forms allows knowing the underreporting due to lack of digitization. One third of the cases can be recovered.

Malaria mortality in Colombia, 1979-2008

INTRODUCTION In Colombia, malaria represents a serious public health problem. It is estimated that approximately 60% of the population is at risk of the disease. OBJECTIVE To describe the mortality trends for malaria in Colombia, from 1979 to 2008. MATERIALS AND METHODS A descriptive study to determine the trends of the malaria mortality was carried out. The information sources used were databases of registered deaths and population projections from 1979 to 2008 of the National Statistics Department. The indicator used was the mortality rate. The trend was analyzed by join point regression. RESULTS Six thousands nine hundred and sixty five deaths caused by malaria were certified for an age-adjusted rate of 0.74 deaths/100.000 inhabitants for the study period. In 74.3% of the deaths, the parasite species was not mentioned. The trend in the mortality rate showed a statistically significant decreasing behavior, which was lower from the second half of the nineties as compared with that presented in the eighties. CONCLUSIONS The magnitude of mortality by malaria in Colombia is not high, in spite of the evident underreporting. A marked downward trend was observed between 1979 and 2008. The information obtained from death certificates, along with that of the public health surveillance system will allow to modify the recommendations and improve the implementation of preventive and control measures to further reduce the mortality caused by malaria.

Urban malaria transmission in a non-endemic area in the Andean region of Colombia

BACKGROUND Rapid urbanisation in difficult socio-economic conditions such as inadequate housing infrastructure, lack of public services, improper sanitation, and poor water drainage systems in vegetation-rich areas lead to ecological conditions that are conducive to the breeding of mosquitoes and transmission of malaria, in semi-urban and urban settings. OBJECTIVES This study aimed to describe the cases of malaria that were reported in the peri-urban areas of Pereira (Colombia), between 2008 and 2015. METHODS A retrospective study was conducted using data from the Malaria Surveillance System 2009-2015 and an outbreak study (between December 2008 and March 2009). Frequency distributions and summary measures, as well as univariate analysis were performed for all the variables in consideration. The annual parasite index (API) was calculated. FINDINGS Data on 214 cases were obtained from the surveillance system. A majority of the cases were reported in men (63.1%), followed by in children < 15 years (23.8%), and were caused predominantly by Plasmodium vivax (86.0%), with most of the infection occurring in the urban areas (52.8%) of Pereira. The API, by sex and age group, was higher among men ≥ 80 years. The outbreak study reported 14 cases of malaria in rural/peri-urban neighborhoods, and it was observed that the anopheline breeding sites were in close proximity to the houses in these areas. This population did not use protective measures against mosquitoes and chemical control was conducted through residual and spatial insecticide spraying. MAIN CONCLUSIONS This study suggested the presence of autochthonous malaria transmission, in Pereira, between 2008 and 2015, most of which were cases of P. vivax. A greater intensity was observed between 2008 and 2009 when malaria was possibly reintroduced to the region. During the years of the study, a gradual decrease in the number of reported cases of malaria was observed in Pereira, except for the time period between 2008 and 2009 when a spike was noted (estimated using the API); this was most likely caused by an outbreak. Interventions that are more aggressive in nature are required to prevent further malarial transmission and dissemination.