Navarrete et al..

Int J Pediatr Res 2015, 1:2

International Journal of ISSN: 2469-5769

Pediatric Research
Research Article: Open Access

Leptospirosis Prevalence and Associated Factors in School Children

from Valle de Chalco-Solidaridad, State of Mexico
Dr. Joel Navarrete Espinosa1*, MC Beatriz Rivas Sánchez2 and Dra. María Luisa Soriano
Rodríguez3
1
Division of Epidemiology, Epidemiological Surveillance Coordination, IMSS, Mexico
2
Department of Microbiology and Parasitology, Medicine Faculty, UNAM, Mexico
3
Unidad de Medicina Familiar # 180, IMSS, Mexico

*Corresponding author: Joel Navarrete Espinosa, Division of Epidemiology, Epidemiological Surveillance

Coordination, IMSS, Mexico, E-mail: joel.navarrete@imss.gob.mx

and it is now known that susceptibility to the disease is universal and

Abstract happens more frequently as a result of exposure and contact with the
Material and Methods: Cross-sectional study in school children urine of infected pets and vermin [5,6].
8-12 years of age; Leptospira identification tests (IFI and Dark
Field: Microbiology and Parasitology Department, FM-UNAM) were In recent years, an increase in the number of cases reported of
performed and risk factors were researched. Those positive to IFI this disease has been observed worldwide, due to the changes in the
(cutoff 1: 80) and dark field in blood and urine were considered environment and the presence of strong rains and floods, which
positives. Prevalence, prevalence ratios, and multivariate analysis expose the population to water contaminated with urine of sick
were estimated. animals [4,7-10]. In Mexico different studies have been performed,
Results: 220 children were studied; the prevalence of Leptospira with different techniques and cut values, and the prevalence of the
infection was 37% (IFI) and 83% (dark field in blood). The highest infection may reach up to 80% of the general population [11-14].
prevalence was for females, children younger than 10 years old,
children from the 16 de Septiembre school, those who had dogs,
The clinical behavior of the infection presents a large variety of
and those whose pet was allowed inside the house. According to signs and symptoms that are similar in many diseases [15-18]. The
the IFI results, in the final multivariate model the main associated knowledge of the disease is almost exclusively based in the description
risk factors were: parents’ schooling (p < 0.05), belonging to the of acute and severe presentations of the disease (Weil Syndrome).
school 16 de Septiembre (p < 0.05), and allow the dogs inside Nevertheless, leptospirosis has been currently described as a disease
the house (p < 0.05). Factors associated with Leptospira in blood that may be chronically present, with multiple manifestations and
were parents’ schooling (p < 0.05), belonging to the school 16 de complications [19-21].
Septiembre (p < 0.05), allowing the dogs inside the house (p = 0.6).
No association with contact with stagnant water was found. In children, the infection may simulate a number of infectious
Conclusions: Children who live in the Valley of Chalco are
diseases, such as viral meningoencephalitis, pharyngitis, urinary tract
exposed to several factors, exposing them to the transmission infection, mononucleosis, and other [22]. This is especially important
chain of leptospirosis. It is important to continue this research line in the case of hepatitis, for the presence of severe leptospirosis cases
to determine the implications of leptospirosis in this population. To with a fatal ending have been documented, and which were initially
educate to avoid close contact with animals to improve health must treated as viral hepatitis [23].
be permanent.
It is currently known that children are a high risk group for the
Keywords disease, for they are in contact with their pets, especially with dogs
[24] and their urine. The children in Valle de Chalco, Estado de
School children, Prevalence, Leptospirosis, Dark field microscopy,
México, are in addition exposed to frequent and large floods and thus
Immunofluorescence (IFI)
to contact with stagnant waters, increasing the risk for infection.
Although studies have been performed in the general population,
Introduction and being considered an occupational-type disease [25], children are
Leptospirosis has been considered a zoonotic disease distributed almost always excluded; in the same way, most of these studies have
worldwide and of occupational type, usually in adult population and been performed in diseased persons in acute state, and the infection
predominant in tropical regions [1-3]; almost always associated with prevalence in children in unknown and little is known regarding the
poverty [4]. However, this concept has changed in recent decades presence in carriers and/or chronic Leptospira infection in them. In the

Citation: Navarrete EJ, Rivas SB, Soriano RML (2015) Leptospirosis Prevalence and
Associated Factors in School Children from Valle de Chalco-Solidaridad, State of Mexico. Int

ClinMed J Pediatr Res 1:008

Received: September 25, 2015: Accepted: October 09, 2015: Published: October 12, 2015
International Library Copyright: © 2015 Navarrete EJ. This is an open-access article distributed under the terms
of the Creative Commons Attribution License, which permits unrestricted use, distribution,
and reproduction in any medium, provided the original author and source are credited.
same way there is little information about the clinical manifestations interrogans: was used Canicola, Icterohaemorrhagiae, Pomona,
and complications that happen or the factors associated to the Pyrogenes, Ballum, Autumnalis, Muechen, Hardjo, Wolffi, Tarassovi,
infection in the children group. Shermani, Grippotyphosa, Bratislava, and Lai lai, as well as a pull of
9 isolates of Leptospira serovar Pomona obtained from patients with
In this context, it is known that animals that have been infected
chronic leptospirosis and typified by means of monoclonal antibodies
may remain free of symptoms and excrete leptospiras for the rest of
at the International Laboratory of Leptospirosis Reference (WHO/
their life; however, there is not enough information regarding this in
FAO/OIE) in Amsterdam, Holland.
humans, concluding that when humans are infected they may excrete
Leptospira through urine for several months [15]. According to the Norma Oficial Mexicana for Leptospirosis [28]
(Mexican Official Normativity), it was considered as case any child
There are few international research works exploring this fact,
who presented a ≥ 1:80 titers of antibodies and those in whose blood
therefore it was necessary to perform the present study with the
and urine was observed the presence of Leptospira in the dark field
main objective of knowing the prevalence of Leptospira background
test.
infection in the school population (children) in the Valle de Chalco
and which are the main risk factors associated with the infection in For data analyses, the frequencies and percentages were done
this population. Knowing the symptoms associated with the infection after clearing the data base. In the same way, the comparison
in acute phase, and knowing the proportion of children in whom between the proportion of children with and without antibodies
persists the presence of Leptospira in blood and urine, and signs and against Leptospira, was performed, with the socio-demographic and
symptoms associated with this condition were established as specific exposure variables by means of the X2 test and Fisher’s exact test with
objectives of this study, which will allow us estimate the magnitude confidence intervals of 95%, and a value of p ≤ 0.05.
of the problem in a community that might be representative of many
Finally, a logistic regression model was performed with the
others in our country and, at the same time, provide elements for the
variables that resulted significant in the bivariate analysis, using the
diagnosis and treatment of leptospirosis in children.
statistical Stata, version 13.1 package. Under the same procedure a
Materials and Methods model was run considering the presence of Leptospira in blood and
urine in the children in addition to the pathologic background from
To determine the prevalence of Leptospira infection, a cross- the specific interrogatory.
sectional study was conducted from January to November 2014
in children aged 8-12 years in the localities of El Triunfo and San Results
Isidro (Valle de Chalco-Solidaridad), registered in 4th to 6th grades of
In total, 220 school children who accepted to participate were
the following elementary schools: 16 de Septiembre, Sor Juana Inés
studied. The mean age was 10.6 years (± 1.3). Regarding the gender of
de la Cruz, and José María Morelos y Pavón, during the 2013-2014
the children, the highest proportions were females. In the same way,
school year; these were randomly chosen from the list of schools in
the highest percentage of the sample was for children older than 10
the vicinity. The selection of the children who participated in the
years of age.
study was also done through a table of random numbers, based in the
school lists. Once the parents of the children objective of the study The proportion of children originating from Valle de Chalco was
were informed of the importance and the procedures that would be higher, and 90% referred having lived at least 7 years in the locality.
performed, signed consent was required to participate in the study. The percentage of children registered in the 6th grade was higher. The
frequencies of the main studied factors are shown in table 1.
From each child who agreed participating in the study, blood and
urine samples were required. A sample of 5 ml of blood was obtain Regarding personal history of important pathologies in the
from the vein in the left arm with the Vacutainer system; the sample children, 7% expressed having some disease. According to the signs
was drawn by a specialist nurse. The sample was kept in the cold- and symptoms suggestive of leptospirosis, it was found that 12%
chain system, in a Coleman-type thermos, at a temperature between presented an allergic disease to different substances; only 2% referred
2-8°C; it was labelled and foliated according the corresponding having symptoms suggesting Hepatitis. 11% referred excessive fatigue
individual questionnaire. Then a part of each sample was sent to the and 24% referred frequent fatigue; similarly, 15% referred excessive
Parasitology and Microbiology Department of the Medicine Faculty sleepiness and 27% having regular headaches.
from the Universidad Nacional Autonóma de México (UNAM),
The presence of exanthema was documented in 13%, epistaxis in
where the detection of specific antibodies for IFI was performed [26];
22%, bone pain in 23%, abdominal pain in 18%, repetitive infections
additionally, dark field microscopy was performed to every sample to
in superior airways in 15%, conjunctivitis in 16%, and depression in
identify the bacteria y blood and urine [27]. In the same way, another
7%.
portion of the sample was used to perform a general blood exam
by conventional methods, being done at the Unidad de Medicina The averages in weight and size for the children were 41.04
Familiar # 180 from the Instituto Mexicano del Seguro Social (IMSS) kilograms (± 11.9) and 1.42 meters (± 0.11) respectively.
in Chalco, Estado de México, which was used as recruitment center
of the studied population. The blood studies presented the following averages for the total
group of children: erythrocytes 5.2 million/ul. (± 0.35), hemoglobin
A questionnaire was applied for the personal identification of the 14.8 g/dl. (± 0.84), hematocrit 43.1% (± 2.7), and leukocytes 6.8
child, as well as to measure the factors related with the disease: time million/ul (± 1.6).
living in the area, socioeconomic stratus (AMAI index), coexistence
with domestic animals, close contact with pets (hug, kiss, sleep with), The prevalence of leptospirosis with the cutoff IgG ≥ 1:80 was
presence of rodents in the household, if living near a breeding place, 37% (0.37; CI95% 0.28-0.47), this cut was the basis for all analysis. In
and exposure to water during floods. Also an interview was conducted the same way, the prevalence of the presence of the bacteria in blood
to know the history of morbidity in the children. The answers to the by dark field was 83% (0.83; CI95% 0.74-0.90) and in urine 40% (0.40;
questionnaire were obtained from the child by one person of the CI95% 0.30-0.50).
research team, previously trained for such task (epidemiology medic) The highest prevalence was obtained with the dark field test in
in the presence of a parent or tutor, who corroborated, or in its case, blood. The prevalence to each of the main studied factors are shown
corrected the answers given by the child. in table 1.
Since the purpose of the study was the identification of infections In total, 188 children (86%) were positive to the IFI test with cut
that occurred in the past, it was determined to identify the presence of points from 1:20 to 1:640, and 31 (14%) were negative. In the same
IgG antibodies. For the detection of IgG antibodies against Leptospira way, the presence of the bacterium in blood was demonstrated in
interrogans antigens, a reference pull de 14-serovars of Leptospira 48.9% of the children, in blood and in urine in 32.9%, and in urine

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 Table 1: Prevalence of antibodies against Leptospira and Leptospira in blood and urine in the studied children.
IFI (1:80) Dark Field in Blood Dark Field in Urine
Prevalence Prevalence Prevalence

Variables n (%) (I.C. 95%) n (%) (I.C. 95%) n (%) (I.C. 95%)
Sex (n = 220)
Male 103 (47) .30 (.21-.39) 103 (47) .81 (.72-.88) 112 (52) .45 (.35-.45)
Female 117 (53) .43 (.33-.53) 116 (53) .85 (.76-.91) 103 (48) .35 (.26-.45)
Age (n = 220)
˂ 10 64 (29) .43 (.33-.53) 44 (20) .89 (.81-.94) 171 (80) .39 (.29-.49)
≥ 10 156 (71) .35 (.2 5-45) 174 (80) .82 (.73-.89) 43 (20) .47 (.37-.57)
School (n = 220)
16 de Septiembre 110 (50) .53 (.42-.63) 110 (50) .86 (.78-.92) 108 (50) .40 (-30-.50)
José Ma. Morelos 73 (33) .15 (.08-.23) 73 (33) .74 (.64-.82) 73 (34) .34 (.24-.44)
Sor Juana Inés 37 (17) .32 (.23-.42) 36 (17) .92 (.84-.96) 34 (16) .53 (.43-.63)
Socioeconomic level (n = 215)
Middle 92 (43) .33 (.23-.43) 91 (43) .81 (.72-.88) 89 (42) .42 (.32-.52)
Low 123 (57) .41 (.31-.51) 123 (57) .84 (.75-.91) 122 (58) .39 (.29-.49)
Have dogs (n = 213)
No 26 (12) .21 (.13-.30) 33 (15) .91 (.83-.96) 32 (15) .31 (.22-.41)
Yes 187 (88) .40 (.30-.50) 186 (85) .82 (.73-.89) 183 (85) .42 (.32-.52)
Living place dogs(n = 173)
Outside the house 158 (91) .38 (.28-.48) 157 (91) .80 (.70-.87) 154 (91) .44 (.34-.54)
Inside the house 15 (9) .60 (.49-.69) 15 (9) .93 (.86-.97) 15 (9) .27 (.19-.37)
Close contact (n = 187)
No 59 (32) .32 (.23-.42) 59 (32) .88 (.80-.94) 58 (32) .38 (.28-.48)
Yes 128 (68) .43 (.33-.53) 127 (68) .78 (.69-.86) 125 (68) .42 (.32-.52)
Kissing the dog (n = 187)
No 147 (79) .41 (.31-.51) 147 (79) .78 (.68-.86) 145 (79) .40 (.30-.50)
Yes 40 (21) .35 (.25-.45) 39 (21) .95 (.89-.98) 38 (21) .45 (.35-.55)
Contact with urine (n = 187)
No 89 (48) .38 (.28-.48) 89 (48) .82 (.73-.89) 88 (48) .45 (.35-.55)
Yes 98 (52) .41 (.31-.51) 98 (52) .80 (.71-.87) 96 (52) .38 (.28-.48)
Rodents (n = 213)
No 77 (36) .36 (.26-.46) 76 (36) .86 (.78-.92) 74 (35) .43 (.33-.53)
Yes 136 (64) .38 (.28-48) 136 (64) .81 (.72-.88) 135 (65) .39 (.29-.49)

Table 2: Infection by Leptospira cases by IFI (different cutoff values) and Dark Field in blood and urine.
Antibodies against Leptospira
Leptospira in dark field 0 IFI 1:20 IFI 1:40 IFI 1 :80 IFI ≥ 1:160 Total

n (%) n (%) n (%) n (%) n (%)

Negatives 6 (19.4) 4 (7.5) 6 (10.9) 3 (6-0) 4 (13.3) 23 (10.5)
Leptospira in urine 3 (9.7) 7 (13.2) 3 (5.5) 3 (6-0) 1 (3.3) 17 (7.8)
Leptospira in blood (n = 219) 14 (45.2) 24 (45.3) 28 (50.9) 25 (50) 16 (53.3) 107 (48.9)
Leptospira in blood and urine (n = 215) 8 (25.8) 18 (34) 18 (32.7) 19 (38) 9 (30) 72 (32.9)
Total 31 (14.2) 53 (24.2) 55 (25.1) 50 (22.8) 30 (13.7) 219 (100)
IFI = Indirect Immunofluorescense

in 7.8%. Six children (2.7%) were negative to all studies. From the (p = 0.1) and 5.7 (p < 0.05) higher risk for the presence of antibodies
31 children in who the presence of antibodies in blood was not for the Sor Juana Inés de la Cruz and 16 de Septiembre schools,
demonstrated, 25 had the bacteria in blood, urine, or both (Table 2). respectively. Regarding the place where pets live, a 4.3 higher risk (p
< 0.05) was demonstrated for those who referred allowing the dogs
For the bivariate analysis, the presence of antibodies (IgG 1:80)
inside the house, when compared with those who did not have a pet.
and the observing the bacteria in blood and urine were compared
with the main studied variables (Table 3). In relation to the presence of Leptospira in blood, a 3.1 higher
risk (p < 0.05) was found for those with parents with low schooling
The association of the following variables was not demonstrated:
when compared with children with parents with higher schooling. As
flooding of the street where they live, contact with flooding water,
to the schools where children went, a higher risk was found for the
presence of rodents in the house, and walking barefoot.
Sor Juana Inés de la Cruz school (p < 0.05) and 16 de Septiembre (p <
For the multivariate analysis, three models were constructed 0.05) school in comparison to the José María Morelos school. In the
considering the presence of antibodies in blood (IgG ≥ 1:80), the same way, although it was not statistically significant, it was found
presence of the bacteria in blood and urine, using the strongest a higher risk (80%) for those who allowed the dog inside the house
association variables in the bivariate analysis (Table 4). when compared to those who did not have a dog.
To measure the relation with the presence of antibodies in Finally, although the model showed less precision, when
blood, a model adjusted by age and gender was used, using the measuring the relation of the same variables with the presence of
most significant variables found in the bivariate analysis. It was the bacteria in urine, a higher risk (80%) was found for those whose
demonstrated a protective effect for children with parents with low parents had a basic education in comparison with those whose
schooling (p < 0.05) in comparison to those who had higher schooling. parents had a higher education. In the same way, a higher risk was
On the contrary, when comparing the school of the child, and taking demonstrated for the students from the Sor Juana Inés (p = 0.08) and
as reference the José María Morelos school, it was demonstrated a 2.2 16 de Septiembre (p = 0.4) schools in comparison to the students from

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 Table 3: Bivariate analysis for infection by Leptosipira: IFI and Dark Field in blood and urine.
Variable IFI (IgG1: 80) Leptospira Blood Leptospira Urine

OR IC (95%) p OR IC (95%) p OR IC (95%) p

Age of the child

≥ 10 Vs < 10 0.72 0.37-1.41 0.34 0.56 0.21-1.55 0.27 0.72 0.37-1.41 0.34
Gender of the child

Male Vs female 0.58 0.33-1.0 0.05 1.37 0.67-2.81 0.38 0.66 0.38-1.15 0.14
School

José Ma. Morelos 1 1 1

Sor Juana 2.7 1.05-6.9 0.03 3.8 1.1-14.1 0.40 2.1 .94-4.94 0.06

16 Septiembre 6.3 2.9-13.2 0.01 2.2 1.0-4.7 0.03 1.27 0.69-2.36 0.44

Socio Economic Level

Medium Vs Low 1.41 0.80-2.49 0.22 1.2 0.58-2.41 0.64 0.88 0.50-1.53 0.65
Parents’ schooling

Average Vs Low 0.33 0.16-0.66 0.02 1.9 0.81-4.74 0.10 1.7 0.93-3.09 0.08
Have a dog

Yes Vs No 2.43 1.0-5.89 0.04 0.44 0.12-1.55 0.20 1.56 0.69-3.48 0.27
Where do they live

No dog 1 1 1

Out of the house 1.78 0.86-3.70 0.12 0.48 0.17-1.32 0.16 1.59 0.79-3.18 0.18

Inside the House 4.37 1.28-14.8 0.01 1.67 0.18-15.5 0.65 0.75 0.20-2.75 0.66
Kiss the dog
1
No Dog
0.5 0.17-1.4 0.19 0.8 0.11-6.3 0.9 0.7 0.25-1.7 0.4
No Kiss
1.3 0.62-2.7 0.50 0.2 0.04-0.81 0.02 0.8 0.40-1.7 0.7
Kiss

Close contact with the dog

No dog 1

No close contact 0.4 0.15-0.88 0.02 4.4 0.98-19.5 0.05 0.71 0.32-1.6 0.41
Close contact 0.6 0.33-1.2 0.16 2.1 0.86-5.13 0.10 0.83 0.44-1.6 0.56

Table 4: Multivariated model for infection by Leptospira* with IFI and Dark Field in blood and urine.
Variables Categories IFI 1:80 Dark Field in blood Dark Field in urine
OR IC 95% p OR IC 95% p OR IC 95% p
Parents’ Schooling Average Vs Basic 0.4 0.18-0.80 0.01 3.1 1.16-8.21 0.02 1.8 0.92-3.30 0.08
School José Ma. Morelos 1 1 1
Sor Juana Inés 2.2 0.80-5.93 0.12 5.2 1.31-20.3 0.01 2.1 0.89-5.13 0.08
16 de Septiembre 5.7 2.6-12.5 0.01 3.5 1.50-8.14 0.01 1.4 0.70-2.59 0.37
Where do dogs live Doesn’t have dog 1 1 1
Outside the house 1.2 0.49-2.7 0.75 0.4 0.15-1.32 0.14 1.6 0.77-3.48 0.2
Inside the house 4.3 1.1-16.9 0.03 1.8 0.17-17.5 0.62 0.8 0.20-3.05 0.73
*Adjusted by age and sex

the José María Morelos school, although the statistical significance and their excrete (urine), are related with the presence of the infection
was marginal. On the contrary, no association significant was found in children [22,23]. This is more evident when considering that as a
with the place in which the pet lives (Table 4). complementary part of the study, a group of children who referred
having a dog in the house was selected to take samples of the pet,
Discussion and by means of dark field analysis, find the presence of Leptospira
There is a relation between the results of the present work with in blood. From 26 sampled dogs, the infection was confirmed in 25;
the information generated by different studies, both national and in the same way, the 26 children who owned these dogs were also
international, and it confirms the importance of leptospirosis as a positive to the test.
public health problem yet to be met. On the contrary, despite the fact that Chalco is a region where
The prevalence of the history of leptospirosis in children living floods occur annually due to the overflow of sewage canals adjacent
in Chalco, Mexico state is high and even higher than that reported in to the area, and thus the high exposure that these population suffers
other works in which symptomatic children with a probable diagnosis with stagnant and residual waters, we were unable to prove this as a
of Leptospira [11] have been studied. However, according to what risk factor, as it has been demonstrated in other researches [25,29,30].
is stated in some studies and similarly to those studies performed Nevertheless, the closeness with the sewage canal (Figure 1) and the
in endemic areas, most of the studied children were anicteric, background of a higher frequency in floods in Sor Juana Inés de la
asymptomatic or presented undifferentiated symptoms during the Cruz school, as well as a higher proportion of children with pets,
infection in the acute stage [15], for they did not manifest any typical and a higher number of these reported by the children in the 16 de
symptomatology associated with the acute stage at the time of the Septiembre school, could explain the higher risks found in these
interview. Consistently with that reported in other works, it was schools. In general, the found prevalence place Chalco area as an
demonstrated that the contact with domestic animals, especially dogs endemic area for leptospirosis.

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 Figure 1: Valle de Chalco-Solidaridad location in México.

On the other hand, as it is shown on table 2, its noteworthy y Vivienda 2010), the proportion of children between 6 and 14 years
the high proportion of children in whom the presence of bacteria of age that go to a school is of 94%, in such a way that the studied
in blood or urine and positivity, in low titers (49%), to antibodies children may very well represent the child population of this area.
was demonstrated, and even more those in whom the presence of
Another factor that contributed to the limited size of the studied
antibodies in blood was not detected (14%). This last point is highly
sample was the high cost of the tests for the diagnosis of the infection
relevant, for they are infection cases that might be unperceived,
(IFI and dark field). These facts did not allow obtaining a larger
if we only take into account the diagnosis through serology. These sample, enough to identify evaluate more precisely the magnitude
facts could have many implications for the individuals, and it results of association strength with some of the risk factors related with the
fundamentally relevant determining the role that Leptospira plays in infection. Including a higher number of schools and children would
the their health, and also for the conceptualization of these subjects allow decreasing random errors and obtaining statistical significance
as asymptomatic carriers of the bacterium or as carriers of a chronic and more precise trust intervals.
infection, especially considering that a high proportion of the children
(40%) presented the elimination of the bacterium through urine, Similarly, the magnitude and the low risks found in this study
which could represent activity of the Leptospira and potential kidney have a direct relation with the high exposure of all the population to
damage [20,21,31-33]; and even as a possible source of infection [34]. the studied factors of both the infected and the non-infected.
Currently there is the hypothesis that this bacterium could remain for However, the relevance of the research does not reside so much
a long time in the individual and behave as an opportunistic germ. in the risk factors for the infection that, although important, have
If it is true that it is hard to identify Leptospira and obtain a been identified in multiple studies [3,4,15], but in the identification
leptospirosis diagnosis by means of dark field study, and that highly of the proportion of children with infection background, as well as
trained personnel is needed to perform the tests, it is also true that those in whom the presence of the bacterium was identified in blood
the personnel participating in the observation of the samples in this and urine “in a persistent way” without the presence of clinical data
study, is personnel specifically trained in the identification of the [33]. The need to continue this research line to corroborate if this
bacterium in blood and urine, having done this professionally for fact determines a condition that does not represent a hazard for the
many years, performing immune-dye and electronic microscopy, children or it is a preclinical or chronic phase of leptospirosis already
working specifically with leptospiras in national institutions (InDRE, described in studies performed in Mexico by some of the members of
UNAM), making the results totally reliable [35]. our work team [19-21].

One of the limitations we faced in our study was the size of the Other aspect to be considered was the cutoff value (1:80) used to
studied simple, as a consequence of the difficulty to perform this classify the positive according to the official normativity [28], since
type of research due to the operative problems to work with children when we performed the exercise with the lowest cut (1:40) the risk
(blood-sample drawing). In this sense, if it is true that the number of was increased. However, although the risks were low with the cutoff
schools included in the study and the size of the studied sample do not that was used, there was consistency in the findings from other studies
allow to completely generalize the results to all the child population in and it fulfilled the established normativity that defines as cutoff value
Valle de Chalco, for only three schools and a small amount of school ≥ 1:80 titers to consider an individual as infected. Currently, there is
children were studied, leaving aside those who were not in school at evidence that refer infected individuals in acute of chronic stages that
the time of the selection which could, in turn, bias (healthy child) may react without significant increases, depending on the infected
the study, it is also true that the selection of the schools and children strains or the immune response of each individual as a consequence
were done randomly, taking into consideration the total number of of repeated exposure [3,15,20,21].
schools in the area, implying that all the children in Chalco had the This is the first study performed in children apparently healthy
same probability of being included in the study. On the other hand, in a conurbation in our country, with environmental and cultural
according to official national surveys (Censo Nacional de Población conditions that reflect in a representative way what might be

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happening in other areas; especially nowadays, when the close contact 16. Pérez SJ, Colín OJ, Caballero SA, Cuellar EA (2005) Seropositividad
a Leptospiras de pacientes sospechosos de hepatitis viral negativos a
with dogs has substantially increased, corresponding to the concept
marcadores serológicos. Rev Cubana Med Trop 57: 57-58.
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