Tropical cities such as Singapore do not have well-de-
fi ned infl uenza seasons but have not been spared from in-
fl uenza pandemics. The 1918 epidemic in Singapore, which
was then already a major global trading hub, occurred in 2
waves, June–July, and October–November, and resulted in
>2,870 deaths. The excess mortality rate was higher than
that for industrialized nations in the Northern Hemisphere
but lower than that for less industrialized countries in Asia
and Africa. The 1957 epidemic occurred in May and re-
sulted in widespread illness. The 1968 epidemic occurred
in August and lasted a few weeks, again with widespread
illness. Tropical cities may be affected early in a pandemic
and have higher mortality rates. With the increase in travel
and trade, a future pandemic may reach a globally connect-
ed city early and spread worldwide. Preparedness and sur-
veillance plans must be developed to include the megacities
of the tropical world.
Flu; 1957–8, Asian Flu; and 1968, Hong Kong Flu) resulted
in 40 million, 2 million, and 1 million deaths, respectively
(1,2). Their social, cultural, and economic effect has been
best described in North America and Western Europe (3).
Although tropical countries such as Singapore do not
have as well-defi ned infl uenza seasons as temperate re-
gions, they are not spared from the effects of infl uenza (4).
Each year, 20% of Singapore’s population is estimated to
be clinically infected from seasonal infl uenza (5). Deaths
caused by infl uenza in Singapore over the past decade were
≈14.8 per 100,000 person-years, which is comparable to
nfl uenza has had a substantial effect worldwide. The 3 in-
fl uenza pandemics of the 20th century (1918–9, Spanish
deaths caused by this disease in the temperate United States
and subtropical Hong Kong Special Administrative Re-
gion, People’s Republic of China (6). However, the effect
of pandemic infl uenza in tropical cities has not been well
described. This study aims to describe the effect of these
pandemics on Singapore, a global trading city throughout
the 20th century. The lessons learned from the effect and
management of previous pandemics may have implications
for pandemic planning in tropical global trading cities.
To determine the effect of infl uenza on mortality rates
during the pandemic years, we obtained monthly mortality
rate data from various offi cial sources in Singapore. For
the years surrounding the 1918 pandemic, data were ob-
tained from the Annual Departmental Reports of the Straits
Settlements (the British colonies that included Singapore,
Penang, Malacca, and Labuan; the last 3 are now part of
Malaysia), and from the Registry of Births and Deaths,
Singapore. For the years surrounding the 1957 and 1968
pandemics, data were obtained from the Registry of Births
and Deaths, Singapore. These were the only offi cial gov-
ernment departments responsible in the respective years for
the collection and verifi cation of these statistics.
Because tropical countries do not have well-defi ned
infl uenza seasons, methods for the analysis of excess
deaths in temperate countries such as that used by Serfl ing
et al. (7) may not be appropriate because the assumption
of infl uenza seasons in distinct, regular waves may not be
valid. We have thus elected to use direct statistical analysis
of data for the 2 years before and after the pandemic year
to form a regression line with 95% confi dence intervals.
Deaths for each month were then compared with the regres-
sion line. Months for which the mortality rate exceeded the
95% confi dence intervals were considered as those with ex-
1052 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 7, July 2007
Infl uenza Pandemic s in S ingapore,
a Tropic al, Globally Connec ted City
Vernon J. Lee,*†‡ Mark I. Chen,* Siew Pang Chan,* Chia Siong Wong,* Jeffery Cutter,§ Kee Tai Goh,§
and Paul Anath Tambyah¶#
*Tan Tock Seng Hospital, Singapore; †National Healthcare Group,
Singapore; ‡Ministry of Defence, Singapore; §Ministry of Health,
Singapore; ¶National University of Singapore, Singapore; and #Na-
tional University Hospital, Singapore
Infl uenza Pandemics in Singapore
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 7, July 2007 1053
cess deaths, with the excess represented as the actual mor-
tality rate minus the predicted mortality rate.
To provide another perspective of possible excess
deaths for comparison, we used another method described
by Murray et al. for 1918, with a simpler equation to es-
timate excess deaths (8). For 1918, death rates during the
3-year pandemic window were compared with those in
surrounding years, i.e., the average mortality rate for the 3
years before and after were subtracted from the mortality
rate during the 3-year pandemic window.
In addition to statistical analyses, we conducted a
detailed search of peer-reviewed journal articles, gov-
ernment reports, and press articles for the 3 pandemics.
Search results provided comparisons of the mortality rates
in other countries and an overview of the public health
issues and interventions conducted in Singapore and how
they compared with those of other countries and current
The 1918 Pandemic in Singapore
The 1918 Straits Settlements Annual Report described
an infl uenza epidemic in June and July that was relatively
mild, with a high illness rate but a low mortality rate, that
peaked during the week ending July 6 (9). A second in-
tense wave occurred in October and November, leading to
frequent pneumonia and a high mortality rate. It peaked
during the week ending October 26, with 97.6 deaths per
million population (10).
The 1918 Annual Report indicated 844 recorded infl u-
enza deaths. However, the Straits Settlements’ overall an-
nual mortality rate was “43.85 per thousand in 1918 when
the infl uenza epidemic struck the country” (10). This is in
contrast to the immediate prepandemic and postpandemic
years from 1915 to 1921, when mortality rates ranged from
29/1,000 to 37/1,000 population. The excess mortality
rate within the Straits Settlements in 1918 was therefore
Figure 1 shows that the excess mortality rate of the
epidemic in Singapore alone, as calculated by our method,
was 7.76 per 1,000 (2,870/369,800) during May–June and
October–November 1918. Using the formula of Murray et
al. (8), we calculated the excess mortality rate for Singa-
pore during the pandemic years of 1918–20 to be 1.80%
(18/1,000, or 6,656 deaths).
The excess mortality rate for Singapore during the
1918 pandemic years was higher than rates for most indus-
trialized countries such as the United States and those for
western Europe (Table), but lower than rates for African
and Asian countries such Kenya, South Africa, India, and
the Philippines. The excess mortality rate of 1.80% for Sin-
gapore was higher than the global average rate of 1.06%
and higher than the rate for other Asian countries such as
Taiwan (1.44%) (8).
To reduce the effect of the pandemic, the government
used available evidence to institute a series of preventive
measures. The government and physicians advised infected
persons to isolate themselves and seek treatment, to dis-
infect the fl oors of public premises daily, and, during the
second wave of the outbreak, to avoid crowded places (16).
Suggestions were also made to restrict or prohibit visit-
ing of hospitalized patients, and schools were closed for a
week at the peak of the second wave (16). Recommended
prophylactic measures included reducing the amount of fa-
tigue and maximizing ventilation.
By the end of November 1918, the epidemic was over
in Singapore, although the media still reported the dis-
ease in Indonesia, New Zealand, South Africa, Japan, and
other regions. There were no local reports or evidence of
a third wave similar to that in temperate countries in early
The 1957 Pandemic in Singapore
The media declared the 1957 pandemic as the “worst
ever in colony [Singapore] history” (18). The outbreak
was fi rst recognized at the end of April and early May and
was purported to have spread through Hong Kong from its
origins in northern Asia (19). By May 5, the outbreak had
become an epidemic, reaching its peak in mid-May and ta-
pering off by the end of the month (20). In May, 77,211
(47.6%) of 162,093 patients who came to government and
city council clinics were treated for infl uenza; 326 required
hospital admission, and 28 deaths from infl uenza were re-
corded (22 from pneumonia and 6 from cardiac complica-
tions) (20). On the basis of monthly mortality rate reports
(Figure 2), an excess mortality rate of 0.47/1,000 occurred
in May 1957. This represented 680 deaths in a population of
1,445,900. There was another small peak of excess deaths
in October 1958, although this was only slightly above the
Figure 1. All-cause monthly mortality rates, Singapore, 1917–1919.
1054 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 7, July 2007
During the 1957 epidemic, the government focused
on public health measures, including closure of schools for
almost 2 weeks because of illness and absenteeism. The
public was advised to keep away from crowded places (20),
and the slogan “no movement of persons – no spread of in-
fl uenza” was professed (21). At healthcare facilities, elec-
tive surgery was minimized to release staff to manage the
epidemic. School health clinics, maternal and child health
clinics, and voluntary clinics were set up as infl uenza treat-
ment centers (20). Although no port quarantine measures
were required by law, the airport health offi cer checked
outward-bound passengers for airlines upon request. Simi-
larly, 1 shipping line screened all passengers boarding their
ships, and those who failed screening were denied embar-
The 1968 Pandemic in Singapore
The 1968 pandemic was the mildest of the 3 pandem-
ics; the epidemic in Singapore occurred in early August
and lasted for a few weeks. The virus was believed to have
spread from a major outbreak in Hong Kong (22).
The outbreak in Singapore peaked August 16–25. At-
tendance at outpatient dispensaries increased over a 2-week
period, and at the peak daily attendance increased 65%
from 6,052 to 9,966 (23). On the basis of monthly mortality
rates (Figure 3), the excess mortality rate was 0.27/1,000
(543/2,012,000) during August and September 1968. Ex-
cess deaths peaked again in May and June 1970, which
mirrored a possible second pandemic wave, as reported
worldwide in 1969–70, although the lower second wave ex-
cess mortality rate was similar to rates in the Americas and
different from rates in Europe and Asia (24). The excess
mortality rate for 1970 was 0.15/1,000 (309/2,074,500).
The 1968 epidemic caused substantial illness and ab-
senteeism from work. However, because of the relatively
mild and short epidemic, no substantial measures were ad-
opted. The Ministries of Education and Health considered
the closure of schools but decided against it because of the
waning of the epidemic (25).
Excess mortality rates vary according to the method
used for calculation and sources of data, facts that reiter-
ate the diffi culty of conducting historical estimates. Never-
theless, the estimated number of infl uenza deaths (2,870–
6,656) in Singapore in 1918 exceeded the offi cial report
of 844 infl uenza deaths. The 1918 Annual Report admit-
ted that the latter number poorly represented actual deaths,
which it estimated more accurately at 3,500 (9). The 1921
Annual Report added that many deaths reported as pneu-
monia were due primarily to infl uenza (10). This showed
that tropical Singapore had mortality rates comparable to
or exceeding those of temperate regions (Table). Similarly,
the calculated excess deaths of 680 in 1957 exceeded the 28
recorded infl uenza deaths.
The excess mortality rate for Singapore (Table) sup-
ports the hypothesis that income levels and development
were negatively correlated with infl uenza mortality rates
(8,26) because Singapore was less industrialized than
many industrialized Western cities and nations in the early
20th century. However, Singapore, as a main trading city,
was relatively more industrialized with a proportionately
smaller rural population, and thus had lower mortality rates
than did neighboring countries such as India and the Philip-
pines (Table). Even in Singapore, attack rates were lower
for Europeans and Asians with higher socioeconomic sta-
Table. Estimated deaths and mortality rates due to influenza during the 1918–1920 influenza pandemic
Country No. deaths (in 1,000s)
United States 402–675
Ceylon (Sri Lanka) 51.0–91.6
The Philippines 81.0–288
South Africa 300
British Honduras (Belize) 1.01–2.00
Trinidad and Tobago 0.30–1.00
Mortality rate (per 1,000), %
Infl uenza Pandemics in Singapore
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 7, July 2007 1055
tus (6.0%–20.4%) than for persons with a lower socioeco-
nomic status (29.0%–29.8%), which suggested that socio-
economic status had a possible role in disease transmission
(19,27). Another possible explanation is that those who
were more educated were also more receptive to public
health messages, which reduced disease transmission.
Using the formula of Murray et al. for the 1918–20
pandemic, we determined that the excess mortality rate
for Singapore was higher than the global average rate. Be-
cause the Singapore epidemic occurred early in the global
pandemic, this fi nding corroborates the suggestion that
early epidemic centers experienced higher mortality rates
(8). This is also evident when one compares the mortality
rates for tropical countries such as Ceylon (present day Sri
Lanka) and Singapore with rates for tropical Caribbean is-
lands (Table). During the second wave of the pandemic in
Spain in October 1918, Asian nations such as Ceylon and
Singapore also reported similar epidemic recrudescence in
early October (28). By the end of the second wave of the
pandemic in Singapore, there were still reports of infl uenza
in Malaysia, Indonesia, New Zealand, and Japan (9,29).
This fi nding also suggests that nations are at high risk of
acquiring early infection and could act as sentinels for the
The effect of all 3 pandemics was felt across Singapore.
However, reported overall mortality rates of 43.85/1,000 in
1918 were comparable to “46.46 per thousand in 1911, a
very malarious year” (10). Deaths during the fi rst epidemic
wave were initially attributed to malaria (30). The 1918
pandemic also had a variable effect in US possessions in
tropical regions (3). The early effect from the 1918 Sin-
gapore epidemic may not have been noticeable because
of the nonseasonal nature of infl uenza in the tropics (4) or
because of the high background mortality rates from in-
fectious diseases and other causes in Singapore. Although
excess deaths in 1918 were substantially higher than excess
deaths in 1957, the relative change in mortality rates was
similar; peak monthly mortality rates were twice baseline
mortality rates for both periods (Figures 1, 2). The 1918
baseline mortality rate was 4× higher than the 1957 rate,
and the decrease in the baseline mortality rate was largely
due to improved socioeconomic conditions and control of
infectious diseases such as malaria. With the low baseline
mortality rate for modern cities, the effect of a pandemic,
however mild, may be noticed (the Singapore media de-
clared the 1957 pandemic as the worst). Although studies
suggest that pandemic mortality rates will be higher for in-
dustrialized countries (8,26), if a pandemic were to fi rst ap-
pear in less industrialized regions with high baseline mor-
tality rates, the pandemic might be missed or dismissed as
yet another spike of endemic infectious diseases during the
initial epidemic phase until deaths increased.
Apart from illness and death, subpopulations were also
severely affected by the pandemics. In 1957, the closure of
670 schools affected 262,000 students who required alter-
native care and education. Commercial fi rms reported staff
absenteeism of 10%–30% (31). Clinics were frequently
overwhelmed, and available healthcare workers were re-
called to cope with the increase in infl uenza patients. How-
ever, healthcare workers were at high risk for infection
(14,31). In 1918, 12 (63%) of 19 nurses at the Singapore
General Hospital were concurrently ill (32); in 1957, 25%
of the nursing staff in Taiping (a Malaysian town) were ill
(33). Healthcare workers were stressed as they coped with
personal illness and increased numbers of patients.
Although more is now known about infl uenza pathol-
ogy and epidemiology, in 1918, infl uenza was correctly
reported as being highly infectious and spread by breath-
ing, coughing, and spitting, and having an incubation pe-
riod “from a few hours to three days” (34). Even with the
knowledge gap, measures such as respiratory hygiene, so-
cial distancing, and disinfection were promoted (16,19). In
the recent World Health Organization recommendations
for pandemic infl uenza, respiratory hygiene has been en-
couraged as a routine preventive measure (35). Social dis-
tancing and disinfection may also be considered to reduce
its effect, depending on severity and transmission of dis-
ease, to reduce its effect, although defi nitive evidence is
Figure 2. All-cause monthly mortality rates, Singapore, 1956–1958.
Figure 3. All-cause monthly mortality rates, Singapore, 1967–1970.
1056 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 7, July 2007
lacking (35). The effect of school closures remains unclear.
Ferguson et al. suggested that closure of schools does not
substantially reduce overall attack rates but does reduce
peak attack rates (36). Germann et al. suggested that school
closures may be effective if conducted early in pandemics
with low reproductive numbers (low Ro values) (37). How-
ever, interventions such as travel restrictions and border
controls have been shown to be not feasible (36). Although
some of these measures may reduce illness and death, they
have to be weighed against productivity losses and socio-
economic effects of the interventions.
With the increase in travel and trade, a future pandem-
ic may reach a globally connected city before preparedness
plans can be fully activated. The 1918 pandemic is thought
to have originated early in the year and had spread to Singa-
pore by June. Another globally connected city, New York
City, also showed an early wave in February–April 1918
(38). The 1957 and 1968 epidemics arrived weeks after
their suspected origins in northern Asia because of travel
from Hong Kong, another globally connected city (21,23).
These type of cities are also the focal point of spread, as
shown by the spread of infl uenza from Singapore to India
in 1957 (39).
Mortality rates suggest that the 1918 epidemic in Sin-
gapore may have occurred in May, which is earlier than in
offi cial reports (Figure 1). This fi nding suggests the possi-
bility of late recognition. Delayed recognition must be con-
sidered even in this modern age. In 2003, the severe acute
respiratory syndrome (SARS) epidemic reached Singapore
within weeks of its appearance in the southern part of the
People’s Republic of China but remained undetected. Two
of the 20th-century infl uenza pandemics and the SARS epi-
demic are believed to have originated from farms in eastern
Asia. SARS was fi rst detected in Foshan, quickly spread to
Guangzhou City (a major regional trading hub), to Hong
Kong, and then to the rest of the world. A global surveil-
lance effort is therefore critical to enable prompt activation
of pandemic plans. This effort should include frontline sur-
veillance of farms in eastern Asia and secondary surveil-
lance of major Asian cities.
Trading hubs may be affected early in the course of
a pandemic and show higher mortality rates. The megaci-
ties of Asia, Africa, and Latin America are now extensively
involved in global trade and travel networks and are more
likely to be affected by a pandemic. However, infl uenza is
a diffi cult surveillance target, with an accuracy of clinical
diagnosis in 1968 of only ≈66% (40). A good laboratory
surveillance network in major cities is therefore critical to
enable accurate diagnosis and virus identifi cation.
This study has some limitations. Mortality rate data in
Singapore, although of good quality because of the small
size of the country, were available only from limited sourc-
es. We have attempted to use estimates from other govern-
ment agencies such as the health department and ministry
of health. Weekly data would have provided better infor-
mation, but quality data were available in the press only for
certain weeks, which we have presented.
Globally connected cities will be especially vulnerable
to a future pandemic, and preparedness plans must be de-
veloped to include the megacities of the tropical world. The
20th-century pandemics swept through Singapore within 4
weeks; future plans must include such a possibility over
a similarly short duration. Public health measures such as
surveillance and preparedness plans must be formulated to
slow the spread of a pandemic and mitigate its effects.
We thank Gina Fernandez for kind assistance and our col-
leagues at the Communicable Disease Centre, Tan Tock Seng
Hospital, and the Ministry of Health, Singapore, for support.
Dr Lee is a preventive medicine physician with the Singa-
pore Ministry of Defence, the Communicable Disease Centre,
Singapore, and the National Healthcare Group, Singapore. His
research interests include emerging infectious diseases prepared-
ness, health economics, and health services research.
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Address for correspondence: Vernon J. Lee, Block 802, Communicable
Disease Centre, Moulmein Rd, Singapore 308433; email: vernonljm@
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