PUBLIC HEALTH
THE
EPIDEMIOLOGY
AND
INVESTIGATION
OF
HOSPITAL-ACQUIRED
STAPHYLOCOCCAL
DISEASE
IN
NEWBORN
INFANTS
Andrew C. Fleck, Jr., M.D., M.P.H., and Jerome 0. Klein, M.D.
Department of Health, State of New York
I)r. Fleck is Epidemiologist, New York State Department of Health.
I)r. Klein is Epidemic Intelligence Officer, Communicable Disease Center, Public health Service, United States l)epartment of Health, Education and \Velfare (assigned to the New york State
Depart-inent of Health).
ADDRESS: (A.C.F.) 84 Holland Avenue, Albany 8, New York.
CONTRIBUTOR’S
SECTION
1102
PEnIAr1IIcs, I)ecembcr 1959
T
HE PROBLEM of hospital-acquiredstaph-ylococeal disease presents singular
fea-tures to the epidemiologist. The parasite can be demonstrated to be widely dispersed in the hospital environment, but produces clinical disease in only certain classes of patients, such as infants, nursing mothers and debilitated. Rogers’ explained this
phe-nomenon when he stated that “major
altera-tions in local and systemic resistance are necessary before staphylococci can invade and actively multiply within human tis-sues.” Since the true determinate of the
disease event is the host susceptibility and
IlOt the presence of the pathogen, the actual presence of one of the various possible
staphylococcal sources and routes of
trans-mission may or may not cause an epidemic,
depending on the class of susceptibles cx-posed. Newborn infants constitute only one
d)f these classes. The newborn infant has a
susceptibility to staphylocoecal disease epi-demiologically manifested by lesions of the
skin and breast. Post partum, mothers have a local susceptibility of the breast tissue. Patients with influenza have a susceptible respiratory tract. As a consequence, the
epi-demiology of staphyloeoeeal disease of the newborn infant probably differs from the epidemiology of staphylococeal disease in otiler classes of suseeptibles.
The present discussion is limited to the
epidemiology of disease in newborn infants.
Tile material is drawn from investigation of
nursery outbreaks in New York State and
a review of the literature.
CLINICAL MANIFESTATIONS
The development of any stapilylococeal lesion in a newborn infant is potentially
dangerous. Trivial disease is sometimes
fol-lowed by chronic furunculosis, staphylococ-cal pneumonia, septicemia or death.
The early lesions in infants affect the su-perficial layers of the skin. They consist of small vesicles or pustules surrounded with
a small zone of erythema, and appear most
commonly on the face, buttocks and
inter-triginous areas. Vesicular, crusting,
puru-lent or bullous manifestations of impetigo are also common. Purulent conjunctivitis
has been prominently reported in the
Eng-lish literature. These minor superficial
le-sions most commonly appear on tile third
or fourth day of life (Table I).
The major manifestations are: subeuta-neous abscesses, breast abscesses, pneu-monia and the metastatie lesions of
septi-cemia. Major disease will usually be present in 15% of the total cases in an outbreak of
staphylococcal infection. The onset of sub-cutaneous abscesses has been observed as
early as the third day of life and as late as
TABLE I
INCUBATION PEluoDs OF PUSTULES, IMPETiGO AND
CoNJuNc-rIvITIs IN NEWBORN INFANTS IN Six
OUTBREAKS IN NURSERIES IN NEW YORK STATE
Interval from Birth
to Onset
(days)
Cases
Number Per Cent of Total
0-I si-s 4-5 6-7 8-9 10-11 H-IS OvenS 1 40 37 Fl 4 2 I 8 1.0 38.0 35.0 11.5 3.9 2.0 1.0 7.6
Total 105 100.0
of 5 days to as long as 2 months. In general, infants with major forms of staphylococcal
disease have previously had minor
manifes-tations, such as pustules or impetigo of the skin.
The frequency of occurrence of major
and minor disease manifestations under epidemic conditions is shown in Table II.2h1
SOURCES OF INFECTION
The primary goal of epidemiologic
inves-tigation is identification of the causative
source of staphylococci and the most
prob-able route of transmission to the suscepti-ble host. In order to reach this goal, the
epi-demiologist must study the distribution of disease in the population and not the distri-bution of the bacteria. This concept is often ignored in the literature. Staphylococcal
disease in the infant is a reaction between a specific microorganism and the human host. Studies which consider only the reactions of the host without disease, such as coloni-zation, do not add much to our knowledge
of the epidemiology of staphylococcal
dis-ease. Such studies are essentially baeterio-logic; they are not epidemiologic. In addi-tion to the discovery of a possible source of
staphylococci, it must also be siiovn, at least indirectly, that the source is actually involved in production of disease.
The most commonly demonstrated source of staphylococci is the clinically infected individual, which in the parlance of epi-demiologists is a clinical case as opposed to a healthy carrier. This is most often found
in personnel who have frequent intimate contact with a sizable group of infants. Minor lesions are overlooked many times and may remain unsuspected as a source of an outbreak. In one instance9 a nursery nurse with chronic suppurative sinusitis, pyroderma and furunculosis was
over-looked as a common source for an outbreak
TABLE II
FREQUENCY OF OCCURRENCE OF MINOR AND SEVERE TYPES OF STAPRYLOCOCCAL SEPSIS IN OUTBREAKS
IN Fouit UPSTATE NEW YORK NURSERIES COMPARED TO TEN NURSERY
Our-BREAKS REPORTED IN THE LITERATURE
Type uf ep.ci.
Minor:
Pyoderna
Conjunctivitiu Omphalitis
New York Stale Reported in the Literature
Nurseries
.4 B C D
Total % of Total Reference Number Total % of Total (I) (5) -(4) (5) -(6)
-(7) (5) (9) (10) -(ii) 18 I 53 4 35 -31 -104 5 6 73.0 4.0 5.0 18 -36 -Q 17 64 93 51 21 & -51 I 101 -31 .51 1 I 389 133 I 63.0 1.0 0.3 Severe: Abscess Breast abscess O,teitis
Pneumonia and/or septicemia
-I 4 7 -5 -S -6 I 3 3.0 8.0 ‘t.0 5 -8 3 -6 -7 3 S -S I I 3 -1 35 Q0 1 13 6.0 3.0 0.3 .0
Unclassified I 1 - - 1.0 - - - - 10 - - 16 - - Q6 4.0
for a period of 3 months. Other
investiga-tors ilave similarly ideiltified a clinically’ ttI)parent lesion, often minor in nature, as tile emmon SOIlC( of an outbreak in a
nursery.”
A thorough dild painstaking effort should be made to eliminate tile possibility that a lesion in tile IlurSery personnel may be tile common cause of tile outbreak. A clinical history and a physical examination should l)e obtained for all persons who have
inti-mate contact with all or most of tile infants
IITI One or more nurseries. The most suspect are tilose persons who are in contact, by
virtue of their work, with all infants within
a nursery tllrotigil tile dressing and feeding
of tile infants. Other persons who are in contact VitIl till infants in the nursery but do not feed or clothe infants are less sus-pect.
‘With consideration given to the degree
of intimacy of various groups one can set
up priorities in tile search for a common
source of lesions or carriers. Persons with
limited contact with only a few infants are less probable suspects as sources. However,
tiley may’ serve as sources for introducing
staphylococci.
Staphylococci \Vilich originate from a
Ic-5iOfl as a source, may be spread by direct contact as in kissing or touching the lesion. Indirect contact is also possible where the infective lesions contaminate hands, toys,
surgical instruments or other material ob-jects which ill turn convey tile organisms to
the patient. Direct contact by droplet
trans-mission may also occur by projection through coughing or sneezing.
In addition to tile source lesion, the nursery infants may be maintaining an in-troduced epidemic strain in the nares or throat. The older infants apparently serve
as a source of stapilylococci for new
admis-5iOIl5. The mecilanisnl ‘hereby the new
ar-rivals are infected is not clearly described.
Such a reservoir is usually demonstrated to be I)resent where tilere is a maximum op-portunity for contact transmission as a re-stilt of overcrowding of the nursery and absence of proper handwashing by
person-nd.7’ 8, 11, 17 In this type of situation fllost of tile infants present in tile nursery will be
nasal carriers of the epidemic strain.
Con-comitantly, nursery personnel nay sllO\’
absence, or a minimal level, of nasal car-riage of the epidemic strain.
In one outbreak in New York State’TM the removal of an infant reservoir of
staphy-lococci was accomplished by treatment of
tile infants with nasally applied topical an-tibiotics for a week. The outbreak termi-nated abruptly. The inference was strong
tilat the outbreak was being perpetuated by
a nasal reservoir of staphylococci in an
in-fant. In another outbreak, 55% of the infants were found to be nasal carriers. Tile re-moval of tile reservoir of infection by this same method reduced but did not
termi-nate tile outbreak. This suggests that even though a reservoir in the infants is demon-strated, it may not be a sole operating
cause of an outbreak. Nasal carriage in the infants may only be a reflection of the
dis-ease that is occurring in the environment. In addition to the healthy infant carrier, personnel carriers are potential sources of
staphylococci. During the investigation of outbreaks in Upstate New York, a total of
217 nursery personnel who were in contact with all infants in the affected nurseries had nasal cultures taken. Seventeen (8%) were found to be carriers of the type 80/81 epidemic strain. In almost all instances
tilese carriers vere recent employees who were not present in the nursery at the time
tile outbreak started. This observation sug-gests that personnel carriers of the epi-demic strain may be victims rather than causes of epidemics. Similar findings have been reported Wilicil seem to support this
tileory.” The incrimination of personnel carriers as sole effective sources for nursery
outbreaks or for nasal colonization of
in-fants is not supported by all the available evidence.
Fekety et al.i believed that the removal of personnel carriers controlled an
out-break. However, they also instituted
Rountree et al.bo reported an outbreak
wherein the phage types isolated from le-sions in the infants and from the nares of healthy personnel were tile same. Nasal
treatnlent of the personnel carriers with
antibiotics was followed by a reduction in
the attack rate. Other factors, such as
over-crowding and identification and treatment of lesions among personnel, may Ilave played dominant roles.
A fourth hypothetical source of
epidemic-strain staphylococci is the umbilicus.20
Some authorities have recommended tilat precautionary measures, such as tile
paint-ing of the umbilical stump with antiseptic
dyes, i)e adopted. This procedure does
re-duce the rate at which newborn infants
are colonized with staphylococci, but there
has been no demonstration that this has an
influence on tile attack rate of disease in tile infants. Evidence against tile umbilicus
as a source of infection has been described by Fairchild et al.,21 who found a 30% rate
of umbilical colonization with type 80/81 staphylococci. In a 1-month follow-up of a group of 144 infants, they failed to find any clinical evidence of stapilylococeal disease.
On tile basis of bacteriologic surveys, a
wide variety of fomites Ilave been
sug-gested as sources. Technically such items
are depots and not true sources. Their
staphylocoecal content must be eontinu-ously replenished from iluman sources.
However the literature leaves the reader with the impression that any place or object
sllOWfl to ilarbor staphylococci must nec-essarily be a route by which they spread to
patients.2224 Such bacteriologic evidence does not establisil l fomite as an effective
source. A fomite can only be incriminated 1)y tile epidemiologic demonstration that a
higher incidence of disease occurs among infants in contact \Vltll the fomite than in
infants \VllO have no contact with the
fo-mite. On tile basis of nursery experience,
the evidence available does not support
fomites as an effective source of staphy-lococci capable of producing outbreaks.
The only instance in which we have been able to epidemiologically incriminate a
fo-mite, was in an outbreak caused by
con-taminated circumcision sets. This outbreak
was essentially surgical.
There is a parallel hypothesis that
pro-ioses a multiplicity of contaminated
fo-mites coming into contact with susceptible
infants to produce epidemics. In the
out-i)reaks in New York State in the larger 1105-pitals with more than one nursery unit, we
found tilat tile disease differs significantly
in the way it affects one nursery unit as
compared to another. This is more consist-ent with a lesion or carrier as the source than multiple fomites as sources, \vilich are usually common to all nurseries.
Finally, another Ilypothetical source of
staphylococci is tile air. The increasing in-terest in air as a source has resulted in a large body of scientific literature dealing
with problems of air-sampling, air-condi-tioning, laundry chutes and contamination
of air. As in tile ease with fomites, the dem-onstration of the presence of pathogens in
tile air does not incriminate tile air as an effective source. It must be shown that the distribution of disease in the population at risk follows tile distribution of the air
sup-plies.
MeLeod has noted:25 “Unless it is shown
otherwise, it would appear reasonable to
consider tilat when bacteria in the dried
state are present as general contaminants of
the environment this may have no more significance than as a reflection of the fact that disease caused by them is taking place
in tile environment. It should not be as-sumed that these dried environmental
de-posits have a significant part to play in the spread.”
In two nursery outbreaks in Upstate New York it was possible to demonstrate whether
or not an air source was operative. In one
outbreak in which two nurseries were equally affected, the air-borne route of transmission was eliminated Ofl the basis
that the two nurseries received separate air suI)1)lies. In tile Otiler instance, tile air
sup-ply was common to two Ilurseries but only
one nursery had a significant rate of disease.
transmission in the form of dust and droplet nuclei, but it is limited to cases from burn
dressing-rooms and surgical arenas,
per-haps because a more susceptible portal of entry is present in such cases.
INVESTIGATION OF OUTBREAKS
The epidemiologic method requires that
each infant in the population at risk be
fol-lowed for at least 15 days after birth and be classified either as a case or as a non-ease
of staphylococcal disease. Such a elassifica-tion of the infants at risk should be based on definite clinical criteria of infection
es-tablished a priori. Bacteriologic evidence
should only be used to confirm the clinical
diagnosis. In the investigation one must be
as certain of the absence of disease for a non-ease diagnosis as he is of the presence of disease in a case. The proportion of the group which is ill defines the problem.2#{176}
The development and proper use of van-ous specific attack rates enables one to
de-velop inferential evidence for or against the
various hypothetical sources and routes of
transmission. Rational control efforts are based on such evidence.
Any observed association between higher attack rates and personal factors on envi-ronmental or chronologic factors will pro-vide guidance to the most fruitful areas for
investigation. Conversely, the absence of such associations will eliminate certain lines of inquiry as being unimportant. A few of the factors which should be explored are: the proportion of infants diseased in each
nursery, time relations of onset of
individ-ual cases, common contacts of infants with procedures such as circumcision on persons with lesions or known carriers of the
epi-demic strain.
A search should be made for lesions in personnel as a source. A clinical history and physical examination, with particular atten-tion to the skin and respiratory system,
should be obtained for personnel in contact with the infants.
A bacteriologic and phage-typing identi-fication of all isolates from lesions in infants
and personnel will identify a common
epi-demic strain, if it is present. With proper
application of the epidemiologic method,
the source and route of transmission can be
identified. The most probable diagnosis
serves as the guide for definitive control.
Control by application of measures
sug-gested by epidemiologic findings does not reduce the desirability of general measures,
such as the improvement of hygiene, review and correction of aseptic procedures, and housekeeping practices. These measures
minimize the opportunities for direct and indirect transmission of many diseases. However, the termination of an outbreak
can be promptly achieved if the source and
means of transmission of the causative strain are known.
SUMMARY AND CONCLUSIONS
On the basis of present knowledge, the various sources and accompanying
path-ways by which effective contacts between susceptible infants and the staphylococcus take place in the nursery outbreaks are as
follows: 1) Direct contact with infective Ic-sions; 2) direct and indirect contact spread from the asymptomatic infant carrier to the susceptible infant within the nursery, par-ticularly under conditions of overcrowding
and poor nursery technique.
Personnel carriers, fomites and air-borne
droplet nuclei and dust, as sources of out-breaks, do not command a body of eon-vincing epidemiologic evidence at this time.
The epidemiologic investigation of
cry-acquired disease requires that each
in-fant at risk be followed for a minimum of
15 days. The most probable source and
route of transmission of the causative or-ganism can be identified. Control efforts should be based on the epidemiologic diag-nosis.
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