How efficient is contact tracing in mitigating the spread of COVID-19? a mathematical modeling approach.

Contact Tracing (CT) is one of the measures taken by government and health officials to reduce the spread of the novel coronavirus. In this paper, we investigate its efficacy by developing a compartmental model for assessing its impact on mitigating the spread of the virus. We describe the impact on the reproduction number R 0 of COVID-19. In particular, we discuss the importance and relevance of parameters of the model such as the number of reported cases, effectiveness of tracking and monitoring policy, and the transmission rates to contact tracing. We describe the terms "perfect tracking", "perfect monitoring" and "perfect reporting" to indicate that traced contacts will be tracked while incubating, tracked contacts are efficiently monitored so that they do not cause secondary infections, and all infected persons are reported, respectively. We consider three special scenarios: (1) perfect monitoring and perfect tracking of contacts of a reported case, (2) perfect reporting of cases and perfect monitoring of tracked reported cases and (3) perfect reporting and perfect tracking of contacts of reported cases. Furthermore, we gave a lower bound on the proportion of contacts to be traced to ensure that the effective reproduction, R c , is below one and describe R c in terms of observable quantities such as the proportion of reported and traced cases. Model simulations using the COVID-19 data obtained from John Hopkins University for some selected states in the US suggest that even late intervention of CT may reasonably reduce the transmission of COVID-19 and reduce peak hospitalizations and deaths. In particular, our findings suggest that effective monitoring policy of tracked cases and tracking of traced contacts while incubating are more crucial than tracing more contacts. The use of CT coupled with other measures such as social distancing, use of face mask, self-isolation or quarantine and lockdowns will greatly reduce the spread of the epidemic as well as peak hospitalizations and total deaths.

A fractional-order compartmental model for the spread of the COVID-19 pandemic.

We propose a time-fractional compartmental model (SEI A I S HRD) comprising of the susceptible, exposed, infected (asymptomatic and symptomatic), hospitalized, recovered and dead population for the COVID-19 pandemic. We study the properties and dynamics of the proposed model. The conditions under which the disease-free and endemic equilibrium points are asymptotically stable are discussed. Furthermore, we study the sensitivity of the parameters and use the data from Tennessee state (as a case study) to discuss identifiability of the parameters of the model. The non-negative parameters in the model are obtained by solving inverse problems with empirical data from California, Florida, Georgia, Maryland, Tennessee, Texas, Washington and Wisconsin. The basic reproduction number is seen to be slightly above the critical value of one suggesting that stricter measures such as the use of face-masks, social distancing, contact tracing, and even longer stay-at-home orders need to be enforced in order to mitigate the spread of the virus. As stay-at-home orders are rescinded in some of these states, we see that the number of cases began to increase almost immediately and may continue to rise until the end of the year 2020 unless stricter measures are taken.

Fractional model for the spread of COVID-19 subject to government intervention and public perception.

COVID-19 pandemic has impacted people all across the world. As a result, there has been a collective effort to monitor, predict, and control the spread of this disease. Among this effort is the development of mathematical models that could capture accurately the available data and simulate closely the futuristic scenarios. In this paper, a fractional-order memory-dependent model for simulating the spread of COVID-19 is proposed. In this model, the impact of governmental interventions and public perception are incorporated as part of the nonlinear time-varying transmission rate. In addition, an algorithm for approximating the optimal values of the fractional order and strength of governmental interventions is provided. This approach makes our model suitable for capturing the given data set and consequently reliable for future predictions. The model simulation is performed using the two-step generalized exponential time-differencing method and tested for data from Mainland China, Italy, Saudi Arabia and Brazil. The simulation results demonstrate that the fractional order model calibrates to the data better than its integer order counterpart. This observation is further endorsed by the calculated error metrics.

New Report of Black Leaf Spot Mold (Pseudocercospora fuligena) on Withania somnifera from India.

Withania somnifera (family solanaceae) commonly known as ashwagandha and Indian ginseng, originated in India is one of the most powerful medicinal plants for more than 3,000 years (1). It is commercially cultivated for its roots, a natural rich source of glycowithanolides, tannins, potassium nitrate, etc., which are an anti-inflammatory, anti-tumor, anti-oxidant, anti-ulcer, and regulator of the nervous system and sleep (2). During the monsoon of July 2011, black spots on the leaves of infected plants were observed in the ashwagandha growing Lucknow, Raibareilly, and adjoining areas of Uttar Pradesh province with 10 to 20% disease incidence. Early stage of disease were characterized by the presence of light chlorotic spots on both sides of old leaves that later turned into dark black spots resulting in early defoliation. About 27 samples were collected from different locations of the fields for isolation of the causal organism and microscopic studies. Infected leaves were cut into small pieces, surface sterilized with 1% sodium hypochlorite for 1 min, rinsed thrice with sterilized distilled water, and placed onto potato dextrose agar (PDA) plates. After 21 days of dark incubation at 25°C, 8- to 10-mm grayish-brown colonies were observed. Microscopic studies at early and mature stages of infection showed production of conidia in conidiophores. Conidiophores were mostly 5 to 9, few dense pale brown, simple unbranched, septate, geniculate and 14 to 55 × 3 to 5.5 µm. Conidia were subhyline, obclavate to cylindrical, some were straight to slightly curved, multiseptate, base long obconic to long obconically truncate, and 12 to 85 × 3.5 to 5 µm. On the basis of cultural and morphological studies, the pathogen was identified as Pseudocercospora fuligena (3). The pathogen identity was further confirmed at molecular level using universal primers ITS1/ITS4 through PCR (4). An amplification of the expected size (~550 bp) was generated, eluted from agarose gel by QIAquick gel extraction kit (Qiagen), cloned into pGEM-T Easy vector (Promega), sequenced, and deposited in GenBank (Accession No. KF881898). NCBI BLASTn showed 99% identity with P. fuligena (GU214675) strain CPC 12296, isolated from Lycopersicon sp. Pathogenicity test was carried out on 10 plants of W. somnifera cv. Poshita through two approaches, one using mycelia from culture and another using spore suspension from naturally infected leaves. In the first approach, fungal mycelia were applied onto the healthy ashwagandha leaves, whereas in the second approach, infected leaves were washed with distilled water and spore suspension of 106 spores/ml was sprayed on healthy plants. Plants sprayed with sterilized distilled water served as controls. Inoculated plants were placed in a growth chamber at 28°C under 90% humidity for 3 days. After, pots were placed in the glasshouse at 27 ± 2°C with 70 to 80% humidity for 21 days. Initial symptoms appeared on the 7th day while typical symptoms appeared on all the inoculated plants after 12 to 17 days. Control plants remained free of infection. Re-isolation of the pathogen on PDA fulfilled Koch's postulates. Black leaf mold caused by P. fuligena has been reported on tomato (5). This is the first report of black leaf mould caused by P. fuligena on W. somnifera from India. P. fuligena has the potential to reduce yield of W. somnifera. References: (1) Anonymous. Alt. Med Rev. 9:211, 2004. (2) B. D. Basu and K. R. Kirtikar. Indian Medicinal Plants: Plates, vol. 1-4. Bishen Singh Mahendra Pal Singh, Dehradun, India, 1991. (3) T. C. Wang et al. Plant Dis. 79:661, 1995. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990. (5) S. Yamada. Ann. Phytopathol. Soc. Jpn. 15:13, 1951.

Esophageal tuberculosis: role of endoscopic ultrasound in diagnosis.

Esophageal involvement by tuberculosis is rare and is commonly secondary to mediastinal lymph nodal involvement. Endoscopic ultrasound (EUS) is a good modality for evaluation of both esophageal wall and mediastinal lymph nodes. The objectives were to study the role of EUS in diagnosing esophageal tuberculosis, to differentiate primary from secondary form, and to assess the response. Retrospective analysis of data over 7 years (i.e. from 2003 to 2009) was used. The study was set in a tertiary care referral institute and focused on patients diagnosed with esophageal tuberculosis. Interventions used included endoscopy, EUS, EUS-FNA (fine needle aspiration) followed by antituberculosis treatment. The main outcome measurements were symptoms, endoscopic features, EUS features, pathological yield, and response to treatment. There were 32 cases of esophageal tuberculosis. The primary symptom was dysphagia, and endoscopy showed ulcers in 18/32 (56.25%) and extrinsic bulge in 20/32 (62.5%) in middle one third of esophagus. EUS showed lymph nodes adjacent to esophageal pathology in all cases. Subcarinal region was the most common site of lymphadenopathy and they were matted, heterogeneous with predominantly hypoechoic center. Histopathology of endoscopic biopsy of ulcers and EUS-FNA of lymph nodes provided the diagnosis of tuberculosis in 27/32 (84.35%). All patients were treated with antitubercular treatment and showed good clinical, endoscopic and endosonographic response. This is a retrospective study, and PCR and culture for Mycobacterium tuberculosis were not done. Esophageal tuberculosis does not appear to be a primary disease and is most likely secondary to mediastinal nodal tuberculosis. A conglomerated mass of heterogeneous with predominantly hypoechoic lymph nodes with intervening hyperechoic strands and foci on EUS appears to be characteristic of mediastinal tuberculosis.

First Report of Wet Rot of Withania somnifera Caused by Choanephora cucurbitarum in India.

Withania somnifera (Ashwagandha) is native to India and commercially cultivated for the production of root withanolides that have anticarcinogenic properties. A disease appeared on plantings of W. somnifera during the 2010 monsoon at the CIMAP and in adjoining areas of northern India. Symptoms first appeared as water-soaked lesions on leaves and stems that progressed to a wet rot. Mature lesions harbored black fructifications of the suspect pathogen. Pathogen isolations were done by placing pieces of infected tissues on potato dextrose agar. A fungus tentatively identified as a Choanephora sp. that produced white aerial mycelia that later turned pale yellow was consistently isolated from infected plant parts. Mycelia were hyaline and nonseptate. Sporangiophores bearing sporangiola were erect, hyaline, unbranched, apically dilated to form a clavate vesicle from which arose dichotomously branched distally clavate secondary vesicles. Sporangiola were indehiscent, ellipsoid, brown to dark brown with distinct longitudinal striations, and measured 12 to 20 × 6 to 12 µm. Sporangia were multispored, spherical, initially white to yellow and pale brown to dark brown at maturity, and measured 40 to 160 µm. Sporangiospores from sporangia were ellipsoid to broadly ellipsoid, brown to dark brown, indistinctly striate with fine hyaline polar appendages, and measured 16 to 20 × 8 to 12 µm. On the basis of the cultural as well as morphological characteristics and description in the monograph by Kirk (2), the fungus was identified as a Choanephora sp. The identification was also confirmed by IMTECH, Chandigarh, India with Accession No. MTCC-10731. The species was later characterized as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt (GenBank Accession No. AB470642) by using universal primers ITS-1 and ITS-4. Its sequence comprising of 18S rRNA partial, complete ITS 1, 5.8S rRNA, ITS 2, and 28S rRNA partial was submitted to NCBI GenBank with Accession No. JN639861. Pathogenicity of the fungus was established on five healthy plants by artificial inoculation with spray of an aqueous spore suspension containing 106 spores/ml. Plants sprayed with sterile distilled water were used as controls. Both inoculated and control plants were kept in a humidity chamber (96%) for 3 days and thereafter placed in the glasshouse at 28 ± 2°C. Initial symptoms developed in 2 to 3 days while typical disease symptoms appeared on all the inoculated plants after 7 to 10 days. Control plants were free from infection. The reisolation from artificially infected plants again yielded a Choanephora sp., thus fulfilling Koch's postulates. W. somnifera cultivation has been affected by root rot and wilt caused by Fusarium solani and leaf spot caused by Alternaria dianthicola (3). The occurrence of a Choanephora sp. was reported on periwinkle, petunia (1), and Boerhavia diffusa (4). However, to our knowledge, incidence of this pathogen on W. somnifera has not been reported so far. Thus, wet rot of W. somnifera caused by C. cucurbitarum is a new report from India and worldwide. References: (1) G. E. Holcomb. Plant Dis. 87:751, 2003. (2) P. M. Kirk. Mycol. Pap. 152:1, 1984. (3) C. K. Maiti et al. Plant Dis. 91:467, 2007. (4) N. Singh et al. New Dis. Rep. 23:29, 2011.

Data-Driven Deep-Learning Algorithm for Asymptomatic COVID-19 Model with Varying Mitigation Measures and Transmission Rate.

Epidemiological models with constant parameters may not capture satisfactory infection patterns in the presence of pharmaceutical and non-pharmaceutical mitigation measures during a pandemic, since infectiousness is a function of time. In this paper, an Epidemiology-Informed Neural Network algorithm is introduced to learn the time-varying transmission rate for the COVID-19 pandemic in the presence of various mitigation scenarios. There are asymptomatic infectives, mostly unreported, and the proposed algorithm learns the proportion of the total infective individuals that are asymptomatic infectives. Using cumulative and daily reported cases of the symptomatic infectives, we simulate the impact of non-pharmaceutical mitigation measures such as early detection of infectives, contact tracing, and social distancing on the basic reproduction number. We demonstrate the effectiveness of vaccination on the transmission of COVID-19. The accuracy of the proposed algorithm is demonstrated using error metrics in the data-driven simulation for COVID-19 data of Italy, South Korea, the United Kingdom, and the United States.

Genome-wide identification and characterization of the BES1 gene family in apple (Malus domestica).

As the most important transcription factor in the brassinosteroid (BR) signal transduction pathway, BES1 not only affects growth and development of plants but also regulates stress resistance of crops. The physicochemical properties, gene structure, cis-acting elements and gene chip expression of apple BES1 transcription factors were analysed using bioinformatics, and expression of this gene family was analysed with qRT-PCR. There were 22 members of the apple BES1 transcription factors, distributed on eight chromosomes, divided into seven subtribes (I-VII), and the same subtribe contained the same basic motifs. Gene structure analysis showed that the number and position of exons differed, and there was no upstream and downstream structure. Analysis of cis-acting elements indicated that BES1 transcription factors contain response elements for hormones and abiotic stress, as well as organ-specific elements. Gene chip expression profile analysis revealed that expression patterns of BES1 transcription factors differed in different apple hybrids and different organs. In addition, expression of apple BES1 genes was higher in flowers, young fruits, mature fruits and leaves. qRT-PCR demonstrated that expression of MdBES1 genes was highest 12 h after BR induction. At the same time, there were differences in expression in response to PEG, NaCl and MeJA. This paper provides a theoretical basis for analysis of the biological function and stress resistance mechanism of BES1 transcription factors in apple.

Discrete-time predator-prey model with flip bifurcation and chaos control.

We explore the local dynamics, flip bifurcation, chaos control and existence of periodic point of the predator-prey model with Allee effect on the prey population in the interior of $\mathbb{R}^*{_+^2}$. Nu-merical simulations not only exhibit our results with the theoretical analysis but also show the complex dynamical behaviors, such as the period-2, 8, 11, 17, 20 and 22 orbits. Further, maximum Lyapunov exponents as well as fractal dimensions are also computed numerically to show the presence of chaotic behavior in the model under consideration.

9-beta-D-arabinofuranosyladenine 5'-phosphate metabolism and excretion in humans.

9-beta-D-Arabinofuranosyladenine (ara-A) was converted chemically to the 9-beta-D-arabinofuranosyladenine 5'-phosphate (ara-A-5'-P) and administered i.v. to four cancer patients in seven experiments. Urinary excretion and plasma levels of radioactivity were monitored for 24 hr in each case. Radioactivity present as unchanged ara-A-5'-P, ara-A, and the deamination product of ara-A, 9-beta-D-arabinofuranosylhypoxanthine, was determined. Excretion was, as in earlier studies with ara-A, given i.v., largely as 6-beta-D-arabinofuranosylhypoxanthine. However, in contrast to the 88 to 97% excretion of ara-A and products in 24 hr when ara-A was given by i.v. push, excretion was 41.47 to 79.1% in 24 hr when ara-A-5'-P was given. With the exception of one experiment at a low dose, where plasma ara-A levels were significant for 6 hr, the plasma levels of ara-A were sustained at significant levels for 24 hr after a single dose of ara-A-5'-P. The doses of ara-A-5'-P given were well tolerated by the four patients. Indications are that this derivative provides important advantages (solubility and sustained blood levels) over ara-A.

Elemental and nutritional analysis of sea buckthorn (Hippophae rhamnoides ssp. turkestanica) Berries of Pakistani origin.

Sea buckthorn (Hippophae rhamnoides ssp. turkestanica) is a very important medicinal plant in northern areas of Pakistan. The fruit of sea buckthorn is rich in nutrients and medicinal compounds such as vitamins, carotene, flavonoids, essential oil, carbohydrates, organic acids, amino acids, and minerals. In order to compare various populations of sea buckthorn for chemical composition, eight populations from different areas of northern Pakistan were compared using fruit characteristics. Phytochemical analysis of berries showed vitamin C (250-333 mg/100 g), seed oil (7.69-13.7%), oil in softer pulp (19.2-29.1%), phytosterol content of seed oil (3.3-5.5%), and anthocyanin (0.5-25 mg/L), while the mineral element composition analysis revealed high contents of potassium (140-360 ppm), sodium (20-80 ppm), calcium (70-98 ppm), magnesium (150-240 ppm), iron (40-150 ppm), and phosphorus (110-133 ppm). This study established sea buckthorn berries as a good source of biochemical and mineral elements. The high variation between different populations shows the potential of selecting and breeding of the raw material for various defined purposes.

Common causes of child mortality in Sana'a, Yemen.

OBJECTIVE: To study the common causes of child mortality at Al-Thawrah Hospital, Sana'a, Yemen. METHODS: A retrospective study of 639 children aged 0-14 years, who died in the hospital within a 4 year period. This study was carried out at the Al-Thawrah Hospital, Sana'a, Yemen, between January 2000 and December 2003. Children who were admitted to the pediatric/nursery unit and died in the hospital were included in this study. Data were collected from patient's files, hospital register and death certificate to ascertain the cause of death and their percentage. RESULTS: Out of 4575 admissions to the pediatric unit, there were 639 children deaths (13.96%). Deaths were higher among those <2 years of age. The most common causes of deaths in the pediatric unit were infections (18.1%) followed by respiratory problems (17.7%), central nervous system diseases (12%), renal (9.7%), malignancy (9.5%), shock (7.9%) and cardiac diseases(7.3%). While in the nursery, out of 4182 admissions in the same period, 823 died (19.67%), among these were pre-maturity (47%), birth asphyxia (23.7%), infections (10.9%), congenital anomalies (8.4%), central nervous system diseases (5.3%) and others (4.7%). Postmortem examination was not carried out in any of the cases. CONCLUSION: The percentage of deaths on admission among children is less than it was previously, but remains high. The majority of the causes of death are preventable. Efforts to further reduce the mortality should be directed at prevention and early treatment.

Oxygen modulates the release of urokinase and plasminogen activator inhibitor-1 by retinal pigment epithelial cells.

The aims of this study were to examine the effect of oxygen, in the presence or absence of exogenous growth factors, on the release of plasminogen activators and plasminogen activator inhibitor-1 by cultured human retinal pigment epithelial cells. Antigen and activity levels of urokinase, tissue plasminogen activator and plasminogen activator inhibitor were measured in conditioned media after cells were exposed to three different oxygen environments: hypoxia, normoxia and hyperoxia. Overall proteolytic balance was determined by zymography. The effects of exogenous basic fibroblast growth factor and transforming growth factor-beta were also examined. it was found that retinal pigment epithelial cells released urokinase, tissue plasminogen activator and plasminogen activator inhibitor in measurable quantities. After 48 h, urokinase levels were highest at normoxia, reaching 7.2ng/10(6) cells (+/-2.0 SEM), whereas plasminogen activator inhibitor 1 levels were highest at hyperoxia, reaching 67.5ng/10(6) cells (+/-3.7 SEM). Tissue plasminogen activator levels were minimal (<0.5ng/10(6) cells) and unaffected by both oxygen and growth factors. Overall proteolytic activity was also greatest at normoxia. Fibroblast growth factor stimulated urokinase production dose-dependently, but plasminogen activator inhibitor only minimally. Transforming growth factor-beta stimulated plasminogen activator inhibitor production dose-dependently but urokinase only at higher concentrations. These results suggest that both oxygen tension and growth factors may interact to modulate the proteolytic properties of the human retinal pigment epithelium.

The effect of contrast lymphangiography on localization of 67Ga-citrate.

Oily lymphangiographic contrast material introduced prior to total-body 67Ga-citrate scanning may be responsible for accumulation of the radionuclide within the lungs. The possibility of false-positive examinations suggests caution in the interpretation of the scan which evidences this finding. When possible, gallium scintiscans should be scheduled prior to contrast lymphangiography.

Oxygen modulates the response of the retinal pigment epithelium to basic fibroblast growth factor and epidermal growth factor by receptor regulation.

PURPOSE: To determine if low oxygen affects growth factor responsiveness in retinal pigment epithelial (RPE) cells and if such effects are mediated through changes in cell surface receptors. METHODS: Proliferating human RPE cells were exposed to varying concentrations of exogenous basic fibroblast growth factor (bFGF) or epidermal growth factor (EGF) at different media oxygen tensions (16 to 147 mm Hg) and cell counts determined after 4 days. Receptor expression was determined by affinity cross-linking and saturation binding studies on confluent RPE cultures exposed to varying media oxygen tensions for 2 days. RESULTS: Retinal pigment epithelial cells exhibited a greater proliferative response to exogenous growth factors at hypoxia than at higher media oxygen tensions, and they expressed bFGF and demonstrated that hypoxia caused both an increase in the number of EGF receptors per cell and a shift from low to high affinity receptors. CONCLUSIONS: These results suggest that hypoxia not only can stimulate RPE cell proliferation per se, it also can "prime" cells t respond more markedly to exogenous growth factors. These observations may be important in elucidating the cause of proliferative vitreoretinopathy.

Regulation of placental vascular endothelial growth factor (VEGF) and placenta growth factor (PIGF) and soluble Flt-1 by oxygen--a review.

Morphological studies show poor placental vascular development and an increase in the mitotic index of cytotrophoblast cells in intrauterine growth restriction (IUGR). We hypothesized that the reported relatively high oxygen level in the intervillous space in contact with IUGR placental villi will limit angiogenesis by changes in vascular endothelial growth factor (VEGF) and placenta growth factor (PIGF) expression and function. Western immunoblot analysis demonstrates a diametric expression of PIGF and VEGF proteins throughout pregnancy, with P1GF levels increasing and VEGF levels decreasing, consistent with placental oxygenation. PIGF mRNA and protein is increased in IUGR as compared to gestationally matched normal placentae. Increasing oxygen tension upregulates P1GF protein in term placental villous explants, whereas hypoxia downregulates P1GF and VEGFR-1 (Flt-1) autophosphorylation in term trophoblast choriocarcinoma cell line (BeWo). Levels of soluble Flt-1 (sFlt-1) protein in supernatant of term villous explants were upregulated by 1 per cent hypoxia, whereas hyperoxia (40 per cent) decreased sFlt-1 levels, indicating that under conditions of increasing oxygen tension, PlGF function may remain unopposed. The addition of PlGF-1 to a spontaneously transformed first trimester cytotrophoblast cell line (ED27) stimulated cell proliferation while PlGF-2 had little effect. In contrast, the addition of PlGF-1 had little effect on endothelial cell proliferation while this was inhibited by PIGF-2. Taken together these changes provide a molecular explanation for the observed poor angiogenesis in the pathogenesis of IUGR.

Epidemic non-A non-B hepatitis in urban Karachi, Pakistan.

An outbreak of icteric non-A non-B (NANB) hepatitis occurred in a residential community of urban Karachi, Pakistan, from August 1986 through October 1986. Of the 114 cases reported from this community during the 1986 calendar year, a clustering of 85 cases was seen during the above period. Twenty-seven percent of 226 households and 9% of 1,250 individuals were affected. Five persons were hospitalized and 1 death occurred in a young pregnant woman. Cases occurred predominantly in the less than or equal to 29-year-old age group (72%), with a male:female ratio of 1.8:1. Thirty-four cases occurred singly within households, while in 28 households multiple cases were seen. Analysis of the epidemic curve and intervals of onset of multiple cases within households suggested prolonged common source exposure rather than secondary person-to-person transmission. No single water source was implicated but a contaminated municipal supply was presumed. Information collected from several other communities and from a university hepatitis reference laboratory suggested that the outbreak was part of a larger urban epidemic of NANB hepatitis. Based upon this investigation and data from recently published reports, it is concluded that NANB hepatitis is endemic in Pakistan.

Parasite density and malaria morbidity in the Pakistani Punjab.

The relationship between quantitative Plasmodiumfalciparum or P. vivax parasitemia and clinical illness has not been defined in Pakistan or in other areas where malaria transmission is not highly endemic. Standardized questionnaires were given to and physical examinations and parasitologic tests were performed in 8,941 subjects seen in outpatient clinics in 4 villages for 13 consecutive months in the Punjab region of Pakistan. The results, based on multivariable analysis, showed that a clinical diagnosis of malaria, a history of fever, rigors, headache, myalgia, elevated temperature, and a palpable spleen among children were all strongly associated with the presence and density of P. falciparum or P. vivax malaria in a monotonic dose-response fashion. The malaria attributable fraction of a clinical diagnosis of malaria, and the same symptoms and signs also increased with increasing P. falciparum and, to a lesser extent, P. vivax, parasitemia. Unlike in sub-Saharan Africa, clinical illness due to malaria often occurs in the Punjab among adolescents and adults and in patients with parasite densities less than 1,000/microl. Clinical guidelines based upon parasitemia and symptomatology must be adjusted according to the intensity of transmission and be specific for each geographic area.