Water-borne transmission of chloramphenicol-resistant salmonella typhi in Mexico (página 2)

TABLE-I NUMBERS OF CASES AND ATTAC ATES OF TYPHOID FEVER
BY AGE AND SEX

! Male Female Total

Figures in italic show rate per 100 inhabitants in each
age-group.

TABLE I1–ATTACK-RATES FOR SPECIFIC ITEMS OF FOOD AND
DRINK

Ate nhabitants for females and 1-6 per
100 inhabitants for males,

Most patients lived in the north-east and east of the
town, an area comprising approximately II third of the city,
within which the attack-rate for inhabitants was 4-0 per 100
inhabitants as compared to 2-1 per 100 inhabitants for the entire
town, Individual blocks had attack-rates which varied from 1 per
100 inhabitants to 16'8 per 100 inhabitants. Of the 83 cases
analyzed, 43 (52 %) were clusters with
multiple cases per household, and 40 were isolated
cases.

During the investigation we learned that because of a
defective pump the entire population had been without municipal
water throughout May and between June 10 and June 28. During
these periods the people had used water from the canal without
boiling it or had obtained supplies from trucks bringing water
from distant wells.

The canal itself was subsequently studied, having been
divided for the purposes of investigation into three segments
during its course through the village. The first segment
corresponded to that part of the canal most upstream, the second
to the middle section of the canal, and the third segment to that
part farthest downstream. The banks of the first segment had
extensive accumulations of human feces, lesser degrees of
accumulation were noted in the second, and still less in
the third segment However, in the latter portion of the second
serpent, several! Pipes were discovered to be discharging raw
sewage into the canal from private multifamily
systems.

Analysis of questionnaires completed for both ill and
well inhabitants revealed a differential attack-rate of 26-1 per
100 for those drinking water from the canal as compared to 6-8
per 100 for those obtaining water from other sources (table n).
In contrast, differential attack-rates for water from other
sources and a variety of food and beverages were not
significantly different for those who were or were not exposed to
these items. Most cases lived in the section of the community
adjacent to the third segment of the canal (the segment farthest
downstream).

Of the bacteriologica1 specimens co11ected, samples of
pork, beef, cheese, and milk were a11 negative. An S.
arizona species was isolated from a single specimen of
chicharron (fried pig fat). Specimens of water from the
canal a11 were heavily contaminated with coli forms; however, no
attempts were made to isolate salmone11a from these
specimens.

During the survey many of the people questioned reported
gastrointestinal illness which roughly coincided with the period
of the outbreak. Although no attempt was made to quantify the
incidence of this illness, it was the impression of the
investigators that there was a general increase in the incidence
of gastrointestinal disturbances associated with the
outbreak.

DISCUSSION

The Ciudad Cuauhtémoc typhoid out break is of
interest as an instance of water-borne transmission of a
chloramphenicol/resistant epidemic strain o S. typhi. We
suggest that the water of the canal was contaminated by an
individual (or individuals) infected with the resistant strain
elsewhere in Mexico and that because of the lack of availability
of municipal water the community was infected through the
ingestion of canal water.

The high rates of attack in the inhabitants of the
section of the village adjacent to the portion of the canal most
downstream can be partly explained by greater likelihood of
exposure. '1'his section is the most densely populated of the
village, and the families with the lowest level of income and
education live there. When the municipal water supply was
interrupted, trucks brought water in. In the most crowded
section, however, people had to wait for a long time to get water
from the trucks and many decided to use water from the canal
instead. The low general attack-rate was probably related to low
concentrations of S. typhi in the canal water. The higher
attack-rates in women may have be en related to greater
likelihood of exposure because women were responsible for
obtaining water for the family.

The high mortality-rate was probably related to the lack
of medical care and the frequent use of chloramphenicol despite
the known resistance of the organism to this agent. Unfortunately
we do not know the specific treatment received by those who
died.

The fact that all age-groups were affected and that the
out break ended as soon as the water supply was re-established
supports the hypothesis of the canal water as the vehicle of
infection. Unfortunately S. typhi was not isolated
from· the water nor was it possible to identify a person
(or persons) who served as the source of contamination of the
canal.

Although the epidemic was eased by a strain of S.
typhi resistant to chloramphenicol, a small proportion of
sensitive strains were al so found in outbreaks occurring in
other parts of Mexico produced by this strain (Vi degraded
approaching phage type A), approximately 10% of the isolates were
sensitive to chloramphenicol, most of them belonging to phage
types 26 and EJ. These sensitive strains were probably endemic in
each community before the outbreaks.3, 8

We thank Dr Paul E. Pierce. and Dr Eugene J. Gangarosa,
Center for Disease Control, Atlanta,
Georgia, who made suggestions to improve the fieldwork and data
interpretation; and Dr José Lopez Franchini, Zacatecas
Sate Health Department, for this cooperation.

Requests for reprints should be addressed to A. G. C.,
Instituto de Salubridad y Enfermedades Tropicales,
Carpio 470, México 17,
México.

REFERENCES

1. González-Cortes, A., Heredia-Duarte,
A., Guzmán ~ Baena, J.
Salud Púb. Méx. (in the
press).

2. González/Cortes, A., Besudo, D., Velez V.
   Ibíd. 1972, 14, 697.

3. Besudo, D., Olarte Jorge, Mendoza Hernández
   P., Galindo, E" Carrillo, l., Gutiérrez-Trujillo,
   G., Kumate., J. Bol. ofna. Sanit. Panam. 1973, 74,
   1.

4. Bernard, R. P. J. Hyg., Camb. 1956, 63,
   537.
5. Varela, G., Mendoza-Hernández, P.,
   Vázquez, A., Revta. IInst. Salubr.

Enferm. Trop. Méx. 1956, 18,
33.

6. Gangarosa, J. B., Bennett, V. J., Wyatt, C., Pierce,
P., Olarte, J, Mendoza-Hernández, P., Vázquez, V.,
Bezudo, M. D. J. infec. Dis. 1972, 128,215. 8

7. Anderson, E. S., Smith, H. R. Br. Med. J.
   1972, iii, 329.

8. Center for Disease Control Weekly Reports 1972.
   Morbidity and Mortality, pp. 21, 177, 193,213,239,290, and
   327.

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The Lancet Office

7, Adam Street, Adelphi, London, W.C.2.

Abel Gonzalez

Cortes Rafael Sanchez

Leyva Marina Hinojosa

Enviado por:

Rafael Fragoso