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Pub.Health.Rev., Hugh Pennington; 2003, WHO Bulletin
Excerpt:
"Difficulties in diagnosing smallpox
The Todmorden outbreak illustrated particularly well the
difficulties that attended the diagnosis of smallpox in nonendemic
areas in pre-eradication times. Essentially, because the
disease was not thought to be occurring in the country, its
diagnosis was not entertained. This is understandable in the
cases that developed suddenly, which lacked obvious smallpoxspecific
features, but is less so in others. For example, a doctor
with extensive experience of smallpox considered A.J.?s rash to
be herpetic. Evidently, the same problem of misdiagnosis could
occur in cases resulting from an unannounced deliberate release
of virus today. The diagnostic difficulties enumerated in Ricketts
& Byles? classical early 20th century textbook on smallpox (10)
were due to virological characteristics that have not changed in
the succeeding years. Their statements that ?two thirds of the
errors in the diagnosis of smallpox arise from its confusion with
chickenpox? and ?in every epidemic cases arise at intervals in
which the eruption is so highly modified and the character of
the lesion is so anomalous that there is an inadequate basis for
diagnosis? are still relevant. Even when smallpox was being
regularly imported into Britain it was often misdiagnosed; thus,
Public Health Reviews
764 Bulletin of the World Health Organization 2003, 81 (10)
in describing an outbreak in the English midlands in 1947
Simpson Smith (11) concluded that ?once again an outbreak of
smallpox followed a confident diagnosis of chicken-pox by
competent experts. This also occurred in 1947 at Scunthorpe;
in the Middlesex outbreak of 1944, the Edinburgh outbreak of
1942 and at Birkenhead in 1946.?
What other lessons can be drawn from the Todmorden
outbreak? Lyons & Dixon (9) pointed out in their account of
the outbreak that classical epidemiological methods were only
partly successful in tracking the spread of virus: ?there were
at least five known cases where infection occurred in
individuals who in spite of most heroic investigations could
be found to have no known connection with any other case.?
Nevertheless, they concluded that ?in spite of many
opportunities the spread of infection was more limited than
is usually assumed. High attack rates only occurred in very
close contacts, in the family, among personal friends, or close
contacts at work.? Their figures show that of 39 cases in
total, 17 people contracted their infections in the domestic
setting ? of these, 13 were family members or lodgers and
four were visitors to the sickroom.
Similar findings were made in the classical studies of
smallpox in Punjabi villages by Mack and his colleagues in 1967
and 1968 (12, 13). The villagers probably had similar levels of
immunity to those of Todmorden in 1953; transmission within
the home was so effective that the secondary attack rate among
unvaccinated household members was 88%. Another kind of
?sickroom? transmission not commented on by Lyons & Dixon
but very evident from their account were the infections
contracted in hospital or by health care workers. Six hospital
patients, the postmortem room porter and two general
practitioners who had attended A.J. and N. fell into this category.
Mack?s review of smallpox in Europe 1950?1971 (14), which
considered 45 importations of Variola major, showed that
transmissions in hospital far outnumbered those in any other
category. Of the 680 cases, 339 people contracted the disease in
hospital ? 128 of these were staff, 193 were inpatients and 18
were outpatients, visitors, or in other hospital-related categories.
Twenty other cases in laundry and mortuary workers were also
occupational. Family and other intimate contacts accounted for
147 cases; only 63 cases were infected by casual contacts. Fortyfour
were classified as ?unpredictable?."
Excerpt:
"Difficulties in diagnosing smallpox
The Todmorden outbreak illustrated particularly well the
difficulties that attended the diagnosis of smallpox in nonendemic
areas in pre-eradication times. Essentially, because the
disease was not thought to be occurring in the country, its
diagnosis was not entertained. This is understandable in the
cases that developed suddenly, which lacked obvious smallpoxspecific
features, but is less so in others. For example, a doctor
with extensive experience of smallpox considered A.J.?s rash to
be herpetic. Evidently, the same problem of misdiagnosis could
occur in cases resulting from an unannounced deliberate release
of virus today. The diagnostic difficulties enumerated in Ricketts
& Byles? classical early 20th century textbook on smallpox (10)
were due to virological characteristics that have not changed in
the succeeding years. Their statements that ?two thirds of the
errors in the diagnosis of smallpox arise from its confusion with
chickenpox? and ?in every epidemic cases arise at intervals in
which the eruption is so highly modified and the character of
the lesion is so anomalous that there is an inadequate basis for
diagnosis? are still relevant. Even when smallpox was being
regularly imported into Britain it was often misdiagnosed; thus,
Public Health Reviews
764 Bulletin of the World Health Organization 2003, 81 (10)
in describing an outbreak in the English midlands in 1947
Simpson Smith (11) concluded that ?once again an outbreak of
smallpox followed a confident diagnosis of chicken-pox by
competent experts. This also occurred in 1947 at Scunthorpe;
in the Middlesex outbreak of 1944, the Edinburgh outbreak of
1942 and at Birkenhead in 1946.?
What other lessons can be drawn from the Todmorden
outbreak? Lyons & Dixon (9) pointed out in their account of
the outbreak that classical epidemiological methods were only
partly successful in tracking the spread of virus: ?there were
at least five known cases where infection occurred in
individuals who in spite of most heroic investigations could
be found to have no known connection with any other case.?
Nevertheless, they concluded that ?in spite of many
opportunities the spread of infection was more limited than
is usually assumed. High attack rates only occurred in very
close contacts, in the family, among personal friends, or close
contacts at work.? Their figures show that of 39 cases in
total, 17 people contracted their infections in the domestic
setting ? of these, 13 were family members or lodgers and
four were visitors to the sickroom.
Similar findings were made in the classical studies of
smallpox in Punjabi villages by Mack and his colleagues in 1967
and 1968 (12, 13). The villagers probably had similar levels of
immunity to those of Todmorden in 1953; transmission within
the home was so effective that the secondary attack rate among
unvaccinated household members was 88%. Another kind of
?sickroom? transmission not commented on by Lyons & Dixon
but very evident from their account were the infections
contracted in hospital or by health care workers. Six hospital
patients, the postmortem room porter and two general
practitioners who had attended A.J. and N. fell into this category.
Mack?s review of smallpox in Europe 1950?1971 (14), which
considered 45 importations of Variola major, showed that
transmissions in hospital far outnumbered those in any other
category. Of the 680 cases, 339 people contracted the disease in
hospital ? 128 of these were staff, 193 were inpatients and 18
were outpatients, visitors, or in other hospital-related categories.
Twenty other cases in laundry and mortuary workers were also
occupational. Family and other intimate contacts accounted for
147 cases; only 63 cases were infected by casual contacts. Fortyfour
were classified as ?unpredictable?."