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Transcript
Journal of Public Health Medicine
Vol. 22, No. 1, pp. 116–120
Printed in Great Britain
Outbreaks of influenza A in nursing homes in
Sheffield during the 1997–1998 season:
implications for diagnosis and control
C. A. Read, A. Mohsen, J. S. Nguyen-Van-Tam, M. McKendrick and
G. Kudesia
Summary
Three recent outbreaks of influenza A in nursing and
residential homes in Sheffield were characterized by high
attack rates among both residents and staff, and a high
mortality rate among residents. The epidemiology of the
outbreaks was unusual in that all three occurred towards the
end of a quiet influenza season, against a generally low level
of community activity, and involved strains of influenza
that were not included in the current season’s vaccine. The
outbreak investigation was aided by the use of a novel
rapid diagnostic technique. In future the combination of
vaccination, surveillance, rapid diagnosis and new antineuraminidase drugs should improve prospects for control
of influenza within closed communities.
Keywords: influenza outbreak, nursing homes, mortality,
elderly
Introduction
Deaths from influenza occur predominantly in very elderly
people with underlying ill-health, and the need to improve
delivery of vaccine to these vulnerable groups has previously
been reported.1,2 Nursing homes are considered to be especially
high-risk environments in terms of both the susceptibility of
individual residents and the close proximity of their living
conditions. A review of 41 outbreaks in nursing homes in the
United States revealed an average attack rate of 43 per cent
although rates up to 60 per cent have been reported.3,4 During
the 1989–1990 season in Michigan, USA, < 38 per cent of
nursing homes reported an outbreak of influenza.5 We report on
three outbreaks of influenza A among residents of nursing and
residential homes in Sheffield during the 1997–1998 season,
which was otherwise ‘very quiet’ for influenza. The Royal
College of General Practitioners’ sentinel scheme identified
lower peak and average seasonal rates for ‘influenza and
influenza-like illness’ than in any of the 10 previous winters. An
estimated 680 000 people in England and Wales consulted
general practitioners (GPs) for ‘influenza or influenza-like
illness’ between weeks 40/97 and 25/98, compared with an
estimated 1 120 000 consultations during the equivalent period
in 1996–1997, 800 000 consultations in 1992–1993 and
1 420 000 in 1989–1990.6 All the outbreaks were associated
with a high attack rate in residents and staff, and in one there
was also a high death rate among residents.
Background
The first outbreak occurred in a nursing home (A) of 60
residents and was reported by a GP on 2 April 1998. The GP’s
patient, a resident of the home, suffered an acute respiratory
illness and died of pneumonia; several other residents, cared for
by other GPs, were noted to be unwell with similar respiratory
illnesses. Following a visit to the home by a public health
consultant and an infectious diseases physician the Directorate
of Public Health convened an outbreak management team to
investigate the situation. Pending further information, the
manager of the home agreed to close to admissions.
The first case occurred on 13 March and the second on 21
March. Over the next 4 days, 25 of 30 residents (83 per cent) on
the upper floor of the two-storey home became ill. Over the
following 4 days, 20 of 30 residents (67 per cent) on the ground
floor also became unwell.
Eleven of 73 staff (15 per cent), and several of their
1
Department of Public Health Medicine, Rotherham Health Authority, Bevan
House, Oakwood Hall Drive, Rotherham S60 3AQ.
2
Department of Infection and Tropical Medicine, Royal Hallamshire Hospital,
Glossop Road, Sheffield S10 2JF.
3
Division of Public Health Medicine and Epidemiology, University of
Nottingham, and Communicable Disease Surveillance Centre (Trent), Queen’s
Medical Centre, Nottingham NG7 2UH.
4
Public Health Laboratory Service (at the Northern General Hospital), Herries
Road, Sheffield S5 7BQ.
C. A. Read,1 Senior Registrar, Public Health Medicine
A. Mohsen,2 Specialist Registrar in Infectious Diseases
J. S. Nguyen-Van-Tam,3 Senior Lecturer
M. McKendrick,2 Consultant in Infectious Diseases
G. Kudesia,4 Consultant Virologist
Address correspondence to Dr Cathy Read.
q Faculty of Public Health Medicine 2000
INFLUENZA OUTBREAKS IN NURSING HOMES
Figure 1 Epidemic curves for outbreaks of influenza A in three nursing homes in Sheffield.
117
118
JOURNAL OF PUBL IC HEALTH MEDICINE
immediate family members also reported influenza-like symptoms. One member of staff was admitted to an infectious
disease ward at the local hospital with a clinical picture
suggesting atypical pneumonia. Overall, 46 of 60 residents (77
per cent) were affected, of whom nine died (15 per cent). GP
records showed that 32 of 60 residents (50 per cent) had
received influenza vaccine.
Residents and staff in a further two homes, one residential
home (B) and one nursing home (C) experienced outbreaks of
a respiratory illness commencing on 1 April and 3 April,
respectively (Fig. 1). A total of 16 of 28 residents (57 per cent)
in home B were affected, one of whom was admitted to hospital
with pneumonia.
In home C, 12 of 50 (25 per cent) residents and seven staff
were affected, and two resident’s deaths were attributed to the
outbreak. Over 90 per cent of residents in homes B and C had
received the current season’s vaccine.
In all three homes the clinical picture comprised cough, sore
throat and myalgia with or without pyrexia >37.58C, which
suggested a common aetiology. However, there was no obvious
connection between the homes, and managers of the homes
were not aware of any movement of agency staff between the
establishments.
Methods
The outbreak management team became alerted to the problem
in home A after most residents had become affected. At this
time (week 14, ending 5 April 1998), levels of influenza activity
in the wider community were extremely low. Weekly consultation rates for influenza and influenza-like illness as
reported by the Royal College of General Practitioners’ sentinel
network had fallen to 51/10 000 by week 13 and had not risen
above 100/10 000 throughout the season.7 As the clinical
picture of illness resembled classical influenza, it was important
to secure a definitive diagnosis in case this heralded the onset
of wider community activity. A case was defined as a resident
or staff member with acute onset of respiratory symptoms
including cough, sore throat and myalgia with or without
pyrexia (37.58C). Residents met criteria for sampling if they
had an acute onset of illness that met the case definition within
the previous 5 days and could consent to the investigations. A
clotted blood sample and a naso-pharyngeal aspirate (NPA)
were collected from those patients who were well enough to
tolerate both procedures.
Direct immunofluorescence, rapid and standard viral
culture,8 and serology (complement fixation test) were
employed to establish a laboratory diagnosis of influenza.
Polymerase chain reactions (PCRs) for influenza A and
respiratory syncitial virus (RSV) were performed retrospectively
by the Enteric and Respiratory Virus Laboratory at Central
Public Health Laboratory, Colindale, on the NPAs in all three
outbreaks from which influenza viruses were not cultured.9
Serology was performed on single (convalescent) or paired
(acute and convalescent) sera for adenovirus, Mycoplasma
pneumoniae, influenza A and B, respiratory syncitial virus,
chlamydia, Coxiella burnetii and legionella.
The outbreak control team recommended a range of
measures to limit further spread. All local GPs who were not
already aware of the situation were informed about the
outbreak. The home managers were requested to close to
further admissions until they had had no new cases for 5 days.
Homes were asked to run on their own permanent staff for the
duration of the outbreaks; agency and bank staff were not
permitted to work in the homes and the homes’ staff were asked
not to undertake bank work in acute Trust hospitals or other
residential homes where they might infect other vulnerable
people. Visitors to the homes were warned about the risk of
contracting influenza, and frail elderly visitors and parents of
young children were advised to stay away.
Results
The five NPAs from residents in home A were all negative for
influenza A by all detection methods. However, a serological
diagnosis of influenza A, by complement fixation test, was
made in three out of six residents.
Influenza A was detected in the NPA of two out of three
residents in home B. One was positive by PCR alone, but virus
was cultured from the other and typed as H3N2/A/Sydney/5/97.
In home C virus was cultured in two out of five NPAs, the
virus being typed as H3N2/A/England/577/98 and H3N2/A/
England/1564/98: both are A/H3N2/Sydney/5/97-like viruses
(see Table 1).
Discussion
In 1997–1998, influenza activity was generally low.10 However, consultation rates for ‘influenza and influenza-like
illness’ recorded by the Royal College of General Practitioners’
sentinel scheme and laboratory reports of influenza A infections
to the PHLS Communicable Disease Surveillance Centre
show that what activity there was extended late into the
season.11 At the beginning of the season the influenza A/H3N2
Table 1 Results of serology and virus detection by nursing
home (numbers, with percentages given in parentheses)
Home
Serology
(no. positive/no. tested)
Virus detection*
A
B
C
4/7† (57)
–
–
0/6 (0)
2/6 (30)
1/3 (33)
*Positives defined as positive in one or more of the following: direct
immunofluorescence, rapid culture, standard culture, polymerase chain
reaction.
†Includes one staff member.
119
INFLUENZA OUTBREAKS IN NURSING HOMES
isolates were similar to the Wuhan-like strain included in
the vaccine;12 however, by week 4, 1998, several viruses
characterized as A/H3N2/Sydney/5/97-like had caused outbreaks of respiratory disease in boarding schools.13
We isolated H3N2/A/Sydney/5/97-like viruses from two
homes and obtained serological evidence of infection in the
third. Neither of these very closely related strains was included
in the current vaccine, which comprised an A/Wuhan/(H3N2)like virus, an A/Bayern/(H1N1)-like virus and a B/Beijing/184/
93-like virus.14
The number of samples taken in our population of elderly
residents was limited for several reasons. First, virus culture
depends upon obtaining clinical material (NPAs) from patients
who are acutely unwell. We were alerted to the outbreaks in
each home after most residents had become ill, limiting the
value of more extensive investigations and explaining why we
had no culture positive results from residents in home A. In this
population, some residents were too frail to tolerate invasive
sampling methods such as naso-pharyngeal aspiration. Several
other residents were confused and unable to consent to
investigations.
Influenza vaccine offers 60–80 per cent protection to
healthy adults when vaccine and epidemic strains are closely
related. Studies in elderly care homes in the United States show
a mean protection of only 27 per cent against influenza-like
illness for influenza A (H3N2), and less for influenza B
vaccines.15 Given that the circulating strains in the frail elderly
care home population in Sheffield were poor matches with the
vaccine A/H3N2 strain it is not surprising that the attack rate
and (in home A) subsequent death rate were so high despite at
least 50–90 per cent of residents having received the vaccine.
However, under normal circumstances when vaccine and wild
strains are well matched, the likelihood of an influenza outbreak
within a nursing home is inversely related to the vaccination
rate among residents.16
Assuming that vaccination conferred some degree of crossprotection against A/H3N2/Sydney, differential uptake of
vaccine may in part explain the higher attack rate in home A
compared with homes B and C (see Table 2).
As vaccine offers less than perfect protection, other control
measures for influenza remain necessary in closed institutions.
We have described other measures instituted by the outbreak
control team. It may be difficult to enforce such measures,
particularly the control of staff movement between sectors. In
home A, one-third of the permanent staff were off sick for the
duration of the outbreak.
The team approach we employed together with rapid
laboratory diagnosis provided an opportunity to employ
chemoprophylaxis. The outbreak control team considered the
use of amantadine as chemoprophylaxis but this was rejected
because of its lack of effectiveness if started more than 48 h
after the onset of symptoms, the emergence of resistant viruses
associated with simultaneous use for treatment and prophylaxis,
and potential side effects in a frail elderly population whose
renal function could not be easily monitored.17–20 In other
circumstances use of amantadine is also restricted because of
inactivity against influenza B.21 The prospects for use of
chemoprophylaxis against influenza in closed communities
such as our nursing and residential homes will improve in the
future. The neuraminidase inhibitors, of which zanamivir is the
prototype, are novel agents with enhanced activity against both
subtypes. They have proven clinical efficacy in prophylaxis22
and in the treatment of established influenza, in which they can
reduce the symptomatic period by 1–2 days provided they are
administered within 30 h of onset of symptoms.23,24 Novel oral
neuraminidase inhibitors are currently undergoing Phase II
investigation and may also become valued agents in outbreak
management.25
There will be greater opportunity for using novel chemoprophylaxis in the management of outbreaks in future if early
warning systems are employed. One of the drawbacks of
current surveillance is that reporting in the independent nursing
home sector is not well developed. The outbreak in home A was
well established by the time our outbreak control team became
involved. The subsequent outbreaks in homes B and C were
discovered as a result of deliberate enquiry by the local Nursing
Homes Inspectorate.
Episodes of influenza-like illness are not unusual in elderly
care homes and it is common for the residents in a single home
to be served by many different GPs. This makes the early
detection of outbreaks less likely. Given that we were able to
establish diagnoses within 24 h of sampling and that the
introduction of safe novel therapeutic agents seems imminent, it
may be time to consider how to implement surveillance so that
we identify outbreaks in vulnerable communities in time to
make a difference. The development of local protocols
Table 2 Immunization rate, attack rate and mortality rate by nursing home (values in
parentheses are percentages)
Home
Number of
residents
%
immunized
Residents
affected
Death rate 14 days
or less after
symptom onset
A
B
C
60
28
50
50
>90
>90
46 (77)
16 (57)
12 (25)
9 (15)
0
2 (4)
120
JOURNAL OF PUBL IC HEALTH MEDICINE
(endorsed by primary care groups) for the detection and
treatment of influenza may ensure a prompt and appropriate
response in future.
Acknowledgements
We thank Dr Maria Zambon from PHLS, ERVL, for assistance
with PCRs for influenza A and RSV.
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Accepted on 14 September 1999